Lack of income If you want to invest in Bitcoin for the long term, you must have a source of income that will enable you to use some percentage of your income, let me say 10%. This will enable the investor to be able to DCA with a particular amount regularly and will lead to an increase in his bitcoin portfolio so that during the long run, he can have a significant amount, which he can take profit after the long run when bitcoin has reached his price target. When you don't have a job or a means of income, this will kill your dreams of reaching your Bitcoin target. Some people after acquiring bitcoin to an extent, quit their jobs that pay them, which they used part of it for investing and believe that the price of bitcoin will keep on pumping to survive them, this is another great mistake some newbies make because we need fiat currency if we are investing into bitcoin for our daily use.
Fomo is one of the things that make some people who are not financially stable invest in Bitcoin without proper thinking and strategy because they don't want to miss out on the people who hold Bitcoin. Don't invest in Bitcoin if you know you don't have any source of income because you will end up selling your Bitcoin at a low price when hunger hits you and there is no other money with you to feed, you will have no choice but to sell your Bitcoin to settle your stomach.
Another thing I think that makes some people sell their Bitcoin is the lack of "Bitcoin fundamentals". When people lack Bitcoin fundamentals and they go into investing in Bitcoin, when there is a price drop in Bitcoin they will be afraid that their money is going to zero, and with this fear, they will be pushed to sell their Bitcoin to recover part of their money before it will go to zero.