It's well known that investor's actual returns are much worse than the investments they're holding. How is that even possible?I got rid of a bunch of useless funds recently. Up or down, not performing - gone.
Every investment (even the best investments) will have good times and bad times. If you buy "high performing" investments you may be buying them just before their bad times are about to start. And if you sell investments after a slump you may be selling just when their good times are about to start. You've effectively bought high and sold low.
Yet it's painful to sit and watch as a previously excellent investment slowly grinds its way down. Been there, done that - and hated it.
So what's an investor to do? No-one has perfect knowledge. I try to buy good investments and hold them for the long term. I have a number of investments that I've owned for decades - through good times and bad. My record is 45 years of continuous ownership. That investment has done quite well. Not always top performance but well enough to hold on.
My rule of thumb is to tolerate 3 years of sub-par performance before moving on. And I never look back. Three years may not be long enough but see my comment above on the pain of watching a formerly good investment grind its way down. That's not good either.