I don’t know, but I suspect the proportion of those who are consummate professionals with side projects is greater than those with side projects who are about to crash.

I guess it matters whether those side projects are intrinsically motivated. If you’re just doing it because you’re expected to, I can see it leading to burn out as it’s essentially a side job. But if you’re doing it out of intrinsic interest, it’s more of a hobby that also builds your professional skills