My regrets...
1. I mined Bitcoin back in 2011. I made the decision to stop mining because the value I was mining was getting close to the cost of electricity. At the time, my mid level graphics card mined about 1 BTC every 7 days, and in 2011 the value of 1 BTC was...meh. I regret that I didn't continue mining for longer.
2. I forgot about my wallet, then, a couple of years later, as the price started rising, I sold off the entire proceeds at mtgox. I ended up with about $500 in my account. If I'd waited a few more years, I could have netted over $200,000. I couldn't have predicted the massive increase in value, but it was still stupid to sell 100% of my funds.
So yeah, as a reasonably early adopter, when it was still possible to mine Bitcoin on commodity equipment in a house... I did some dumb things.
.....
I remember reading about a guy who went all in and bought $30k worth of GFX cards and mainboards, on credit. This was probably around 2011-2012, before ASICs were a thing. People said he was crazy.
Following on from this...
It took me a few more years to figure out that miners (especially those who can switch coins easily) are in a unique position: if you ignore capital costs,
your maximum losses are limited to the electricity your equipment consumes. You don't need to risk buying hundreds or thousands of dollars worth of a coin that could crash tomorrow; if the market (or the coin) that you've been recently mining dies, you've just lost the value of the power used to mine it.
I used this epiphany to my advantage in 2017/2018 by finding obscure scrypt coins that were easy to mine. In essence, I was making the profit when I
bought (mined), not when I sold. At that time, my costs were capped at around USD1000 per year, regardless of what I did with the coins I mined.
If I'd thought back in 2011 "this is only costing me a dollar a day, may as well keep going" rather than "hmm, if I don't sell soon I may not cover my electricity costs" then things could have been quite different.