There are advantages with critical thinking, humbleness and willing to learn, and starting out as long as they have discretionary funds. Of course, they might need to figure out how much to start with, yet most people should already have the skills to figure out balances, even though they may need to practice, start out slowly and then adapt their starting out level to their comfort level.
Some folks have absolutely no experience in investing and/or money management, and other people already have some skills and experiences, so their own assessment of their skills and experiences should help them to figure out starting out size, and let's say that a newbie for sure knows that he has $100 per week that he can use to buy bitcoin, yet maybe based on his being new, he purposefully chooses to start out his investment level at $30 per week until he becomes more comfortable to potentially increase the amount to higher levels as his comfort becomes greater.
You’re absolutely correct, people who have the tendency of thinking, and being humble and willing to learn about things, have a high tendency and opportunity of starting in a good way, as long as they’ve an availability of a discretionary income for them to keep buying and accumulating bitcoin, however before getting started with investing in bitcoin you will have to figure out your discretionary income, and also figure out your expenses, how much that you will required for your expenses and how much that would be for leftovers to start buying and accumulating, and also to figure out either to be buying on a weekly or monthly basis.
Just like you have mentioned some folks doesn’t have that ability of critical thinking which would enable them to figure out their discretionary income, and also figure out their expenses, because they don’t have that humbleness and they’re not even willing to learn about things concerning buying and investing in bitcoin, probably because they lacks some skill and basic knowledge on how to go about bitcoin for a long terms purpose, just like you have also mentioned, they can have a $100 leftover after paying for all their expenses, but because they lacks that basic knowledge and skills to invest in bitcoin and probably because they’re scared to get started might decide to start with $50 from the $100 leftover, which is why I feel this situation is all about negligence and lack of awareness and trust in investing in bitcoin.
However for someone who have that zeal and passion to invest in bitcoin would always want to invest their money in bitcoin, which I think it’s not proper to invest all our discretionary income into bitcoin which might be a very awkward thing to do in a long term investment, invest as much as you can afford to loose which is why it’s also important to understand as a beginner that investing in bitcoin doesn’t have a guarantee, but appreciate long term investment with a touch of consistency.