Honestly, it is not a good idea for an investor to sell all their Bitcoin investment, which they have taken much time to accumulate, even if they made a reasonable profit for a particular time. The only good plan is to sell some portion if they have something specific to use the money for at that particular time. However, if they don’t have an immediate need for the money, it is better to continue building their Bitcoin further.
If an investor sells off all their Bitcoin just because they have made some reasonable profits, they will have to start buying again which he has no idea for about the further price of bitcoin. That would be a very poor decision. Bitcoin investment should be a lifetime investment. Once someone has reached their target level of accumulation, the best approach is to take profits when necessary and continue holding.Selling all of one's Bitcoin investment should never be the plan of a serious Bitcoin investor, especially if they aim to invest fo long time.
It would look like a waste of time, if something sell all the Bitcoin in their portfolio after holding for many years, even though it's for 10years and more, It doesn't make any sense, of course an investor has every right to sell some portions or diversify into another good profitable investment that comes up in the future but selling all makes no sense since Bitcoin investment has the potential of lasting for many year "lifetime" as you said, even though no one knows the future yet.
Let's say Bitcoin gets to $1m in 10 - 15 years time and someone sell all their Bitcoin just because they've made lots of profits from it then Bitcoin goes to $1.5m or more such person have sold at lost and would be buying back at a higher price, situation like that is the reason why it makes no sense to sell everything in one's portfolio, something that took years to be accumulated moreover since bitcoin is a lifetime investment it shouldn't even be considered.
Actually you have just spoken my mind on this selling all his Bitcoin at once, no matter how much money you have accumulated in Bitcoin or outside Bitcoin, and think of selling all Bitcoin is the best way, my brother it is not best way, on my own i see all my investment in Bitcoin as an asset, because Bitcoin is my lifetime investment and selling it in a hurry or anytime soon will never come my mind, i will always hodl the dips in long term, so it is very good to always plan ahead of you future, because once you sell up your Bitcoin temptation of the things you will use the money will come immediately as if it was planned and that will make you to start all over again from the cretch and which it will take along time to accumulate, but selling some parts of the investment when you think is due to sell, you can sell some at of it than selling all, and that is why they thread on buy the dip and hodl was created for it to be refreshing our minds on how we should go about our Bitcoin for those that is still coming up.