If you have reached your bitcoin target does not mean that it's selling time, rather you have just transit to your maintenance stage. You can only think of selling part of your bitcoin when you have accumulated more than enough Bitcoin.
After achieving your goal, an investor can certainly sell a portion to enjoy the gains, or plan to reinvest elsewhere, which I think should be done. Because it would not be wise to put all your eggs in one basket. However, that doesn't mean that after reaching your goal, you should sell all your Bitcoin—no Bitcoin holder would want that, especially not me. This is because you would never want to sell a company that you’ve built with your hard-earned money to someone else. Investment is like owning a company or a business. Once established, it will continue to provide you with profits for a lifetime. You could even pass it on to your heirs if they are capable. Just like you would never be willing to sell a company you built with effort, holding onto Bitcoin is like holding a company, and completely selling it might be a wrong decision.
But there are some gains investors don't touch no matter the condition they may find themselves, after achieving their goals because they always believed that something will come up that will draw their attention to invest to increase their wealth, and they will not struggle to get the money because they have the money to create such business.
The moment you sell the company that is bringing profits to you daily or weekly, you will begin to reduce gradually because the profits will no longer come and you will be regretting for not buying BTC as usual. That is why hodling BTC is like a tool investors are using to pull out profit from the market when bull run hit the market, Nobody is hodling BTC to experience lost in the bull run.