Selling and taking profit during the bull run is not ideal because after selling, you might not be able to buy back at the price that you bought before and this will make you have less bitcoin that the initial amount that you had before selling. Meaning that you don't have a bitcoin target and you are not focus on accumulating bitcoin on a long term investment. Another reason why this strategy is not the best is that you will miss out the compounding interest that your bitcoin investment will accumulate for you if you only keep on accumulating till 10yrs time or more. Try and see your bitcoin investment as your life savings and not for profit alone because nobody knows if at the long run it is your bitcoin investment will be the one to take your to the next level in future because there is high possibility that bitcoin price might keep on increasing with timeline. It is better to save for the future than saving to sell and take profit and buy back again. All bitcoin sold can not be bought back easily because of the change in price towards the upside. It is also a bad idea to sell all your bitcoin investment and hold fiat. What is things didn't work out as you planned it after selling, that is when you will regret your action.
You have a point because that has been the challenges most investors normally face because most of them always feel that selling there Bitcoin on a bull Run will give them some sorts of advantage to achieve two things at a time by selling there Bitcoin with the plans of buying back immediately if the price drops down without knowing that it could sometimes be the worst mistake they will ever do because the chances of the price dropping down from the level they sell there Bitcoin may not really be possible were as it could lead them to miss a great opportunity they should have utilized.
So irrespective of the profits an investor should have made on a bull Run shouldn't influence there judgement in times of risking it because is not worth it, so holding should always be taking note of.