~~ because its exchange rate would keep rising.
Bitcoin doesn't always rise its price. There is the time that Bitcoin price tends to drop. It is in bearish season as we are experiencing now.
But when I started spending time with Bitcoiners, attending Bitcoin meetups, and reading books from the Austrian School of economics, I realized that this was not the real point. That is when I finally understood why Bitcoiners say: “Never sell your Bitcoin.”
So, what is the point?
As far as I know, people must sell their Bitcoin if they are investing in Bitcoin. No investors will invest forever, they must have a certain target for taking profits. I'm sure no investment books which tell the readers to hold their assets forever.
Once the Bitcoiners said to not sell the Bitcoin, it means it isn't a proper time for selling. But when it is the right time for selling, I am sure they won't try to prevent us for selling Bitcoin. And you are the owner of your Bitcoin, you must decide it yourself. If it reaches your target, I think you shouldn't doubt to take profits.