I agree with the fact one should hold literally forever. The thing is, big bubbles happen and the opportunity to x5 your BTC by selling on a peak is always there.. but who wants to risk it? you not only need to nail it when selling at a peak, you need to nail it when buying back on a correction.
Just maybe one day it'll hit its eternal September and those who thought they were heroes selling off to buy back lower end up looking like dicks when it don't. Everyone's a trading hero in retrospect and market behaviour is ingrained until it's not.