This is my exact sentiment here buddy, selling all at once is like saying that you are no longer interested in making money or you are saying indirectly that you will be dieing tomorrow, so their will be no point having any Bitcoin anywhere, because even Elon musk the richest man in the world now is still investing, because he is still looking to make more money, so why selling off all your investment and start afresh if he is going to start again at all.
It is foolish to sell your entire investment after the investment period ends. Because you have been investing for a long time and you have kept your holdings until your time limit ends. If you sell your holdings after that, then you will have to start investing again and you will have to wait until your time limit ends to sell your holdings. But if you do not sell your entire holdings, you can sell some amount of holdings during your need period which will be able to meet your needs. If you can keep your holdings in this way, then it will be good for you.
What do you mean by investment period ending? Wait, are you saying someone can invest in Bitcoin and decide from the beginning that he will sell after a given number of years? That is funny because I'm just imagining what he will do if there have not been reasonable profits during that period, will he sell at loss? I don't see this as an efficient way to go about investing in Bitcoin because it has a chance of breeding frustration and loss of confidence and even money. Besides, someone who have this plan may be tempted to invest beyond what he should with the hope that he will recoup his investment when he sell. Some may even go as far as borrowing money to invest which is never advisable.
While investing in Bitcoin, it is good to give some room for time-based growth and not force the market to vomit profits at a set time. This is why it is strictly advisable to only invest discretionary income so that there will be no pressures to sell at a particular time.