At that time, 1,500$ is a big money to buy bitcoin. I can guess that the whole minted bitcoin wasn't worth the 50,000$. If 1btc = 10$ then 50k can buy 5000 btc which was not yet minted maybe.
Maybe he was about to scam you.

If you meet someone who doesn't know that you are a successful investor (doesn't know you in person either) and has little/No knowledge about cryptocurrencies, and you told him your story with bitcoin in early days, do you think he will be convinced to set an investment budget of 50,000$ ?

Do you know how many people had early opportunity with the Bitcoin but missed it? Can you imagine that many of them were already investors and Devs?
No one expected the adoption will be that large.

@Coupable, As at that time, I knew very little or nothing about Bitcoin. Perhaps his intention was to scam me. I can't say for sure but his presentation was quite convincing.

I think the plan was to buy over times, maybe throughout the first 1,2,3 years but he just needed an Investment capital for it.

While the presentation was interesting, the whole thing seemed vague to me, hence the reason i pulled out. 

Of course and it was. A stranger came and told you than a magic internet currency would rise by 10,000,000%. This sounds nothing, but vague.

Look, your reaction was COMPLETELY justified and I'd do the same if I were you. The problem of this missed opportunity lies on the lack of knowledge. You didn't know what was bitcoin. If someone had come to me and said this, I'd definitely search what the hell that thing is, just out of curiosity. (And so did I)

So, I'd say you lost this opportunity not due to your denial of the investment plan, but because you didn't read what it is. If you had read how both bitcoin and our monetary system work, you may had bought few billion sats.

Lesson (hopefully) learnt; stack sats.

Instead of regretting about what was missed out, I believe that we are still having many more opportunities if we plan up for next 10 years. In next 10 years bitcoin definitely will value more than 10 million dollars (this year's speculation is $100k and in ext 4 years it will be 1 million and in 8 years 10 millions dollars). So, planning up from today onward definitely will help anyone.

Even if you are not able to invest any big money right now you can plan up investing on every month so that you can make some decent profit in next 10 years.

I believe most people might have understood the potential of bitcoin right now but the problem with most of the investors is, they are getting excited when they are seeing 2x or 5x profits and then go profit booking or when bitcoin market is falling down for some 25% to 50% then they get panic and then exiting.

You need to trust on the potential of bitcoin for next 10 years so that you can enjoy similar profits.

Well we are all have are share stories about bitcoin in money and we all have regrets about not believing in it earlier, i for one back in 2011 was just in high school and i was always looking for a way to make money from the internet, and one day there was a report in the TV news about a guy using 4 computers to mine bitcoin and make profit from it, the idea intrigued me and i wanted to know more about it, but i didn't have neither the knowledge or the patience and it seemed way to complicated for me so i let go of the idea and moved on with life until five years later when a friend mentioned that he is earning money from it and that is when i know that i missed my chance to make a fortune if i had kept with it, but now i am trying to make up for that mistake by earning and holding bitcoin however i can.

When you missed your opportunity, you don't need to regret for the profit you have Miss for 10 years than to improve in your strategies to recover all that you have loss for the pass. Now that the price of bitcoin is about to increase higher, it will be favourable to those investors who are well prepared for this great opportunity that is about to land in the market.
If you missed the first opportunity because of lack of preparation and research failure. This second opportunity is for those that have the knowledge and experience about this season of profits making.

A lot of people here had an encounter similar to yours regarding Bitcoin but
as @BlackHatCoiner posted it was easy to be skeptical in the early days because
Bitcoin was revolutionary (still is actually!)

@Dripstoil what ever happened to that other oerson who approached you back then?

Regret always come late and you are one of many others who told us today. If you have time to buy that day, I bet you won't be able to stop yourself from selling bitcoin for $100 or maybe you are very lucky only if you forget your wallet for years after the purchase. After all, there have been enough incident where bitcoin users have been scammed (including exchange hacks) since then and you don't seem to want to talk about it. I will never regret it in my life because in fact you and I and other people could still buy bitcoin when it was under $10K last year and make a spread profit of $60K per coin.

Of course, many other forum users besides you feel the same way simply because they missed an opportunity for various reasons. But I'm sure if you keep remembering it it will never be good for your mental health. I barely slept for onenight just because I sold my investment asset for $150 per token in the past which is currently at $4.4K. Since I realized it wasn't a mistake, I forgot about it from then on.

There are greater fools than you.

I am a bigger idiot because I had excellent background to understand bitcoin myself. But bitcoin showed me I am an idiot. It made me humble that way.

I came across bitcoin around 2011-2012 in an emerging financial technology forum that is defunct today. Made a note to myself to read, research and understand the topic. However, never got the time and got carried away with job, family, home, sports, etc. Golden opportunity lost to mine with CPU, GPU and FPGA.

I again got some time from professional life in 2016. This time I finally read Satoshi's paper and understood what it is. Decided to mine. Researched the technical options. Found this forum, coinmarketcap, coinwarz, exchanges. Downloaded the softwares for Bitcoin, Ethereum and other alt coins. But again made a wrong decision. It was the time of S7 and R4. Somehow I decided to go more heavily on GPU rigs. Built several GPU rigs. Then again got busy with the job and did not expand the operation. Did not replenish the GPUs when they died. Since it was challenging for me to handle life and the GPU farm I tried to consolidate by selling smaller gpus to buy larger GPUs to reduce complexity another wrong decision. This way for couple of extended period I was caught on the supply chain hick up of the GPU market when I have sold my existing GPUs and could not replenish the existing rigs because none are available or I was not willing to buy at that price. This Happened for sometime during 2016 holidays to summer of 2017. Since I was not doing this with dedication, there were many extended periods when my rigs were empty. During 2018 crypto winter finally I was able to replenish all my rigs. The people who were consistently after all 2nd hand gpu during this period made a lot of money in 2019 and 2020 and if the GPUs are alive they are making even now. Unfortunately about 50% of my GPUs died by 2020. Few were under warranty but most died just after warranty. So i am watching the best time ever to mine with GPUs passing by while 50% of my rigs are empty. I never upgraded much Asics beyond s9 regularly.

Only one thing positive I was doing is never selling any crypto that I mined. There also I got bombed by some smaller exchanges closing. But at least with whatever hobby level capacity I had I kept mining regardless of price or profitability. The other positive is my son got an excellent understanding of crypto, probability, economics, market, profitability, credit, leverage, negotiation and building computers.          

I am a failure in crypto largely because I failed to recognize the opportunity and focused on my day job, stock trading and kept my mining at the hobby level. If I embraced mining fulltime with all my money and credit then people would be interviewing me by now. Probably should have replenished mining capacity when they died also on a regular basis rather than waiting for the right moment and getting caught on work or supply chain problem.

One thing that caught my attentions was, the person offering him was asking for $50k or nothing, and that's big amount of money. So I have the feeling that person was about to scam you. Why $50k, he knew you were willing to risk $1500 but he was asking a lot. So yes, don't regret your action that day, because it maybe was a blessing in disguise.

@OP, do you know by any chance what happened to this person? Is he still in crypto?

And also, you can always look forward and not backward. You can still invest on this market if you truly believe there is a future in this market.