I don't think that should stop you from planning, but just like death is ultimately inevitable, it is good to be healthily aware of failure (getting punched in the mouth). "Oh well, the movie is going to end, might as well not watch it"
Yeah, being in my 40s and looking at that, my immediate thought was "oh, it seems I'm trying to figure out plan Z, even when I had pretty good plans A and B."
My advice from the other side is that there's too many unknowns to plan out your career. Fields shift in terms of content and culture, and you don't know what you like until you're really in the middle of it.
By a lot of metrics, I've achieved plan A, but found out, after a lot of work, that I am not a good fit for it and that plan B has a lot of similar problems. I never had a plan Z.
I didn't have a plan and things have been going great so far. So it's a little different when you're not in a zero-sum adversarial situation like a boxing ring.