That should be an individual choice whether to sell all or still continue holding. Because every individual has a target and once that target has been achieved and the time to sell has reached then they can sell them. Let me, if bitcoin reached $100k, men I will not lie, I will sell.
Yeah it is the choice of people to decide whether to sell there Bitcoin or to hold them, however it is advised for people to hold there Bitcoin until they have accumulated enough, some people sell there Bitcoin when is not enough and there are many reasons why they do that which are one because of emergency issues when people face some challenges that they need finance in other to settle it but because they have no money or they have spent there savings and still more money is needed so they have no other option but to sell of there Bitcoin in other to get money and settle there problem, and that is why it is always advised to have a strong emergency, reserves and float funds in other to secure one's Bitcoin investment, if you have a strong emergency, reserves and float it will help you settle a lot of emergency issues that comes up.
And two because of Panic and fear, a lot of people sell off there Bitcoin because of fear and this thing happens to newbies especially when there is a fall in Bitcoin price they become afraid and sell of there Bitcoin in other to have some of there money back before they lose all, people who are doing this are just people who don't understand how Bitcoin works if you understand how Bitcoin works you will not bother yourself when there's a dip because is certain that it will rise again.
Bitcoin will hit $100k soon any if you who started accumulating Bitcoin when it was around $40k are free to sell some Bitcoin when it gets to $100k but for those who just started when is $70k now should keep holding even when it hits $100k.
Some people feels it is impossible for Bitcoin to hit $100k and that Bitcoin has reached his growing limit but this is not true Bitcoin will keep growing bigger and better.