Ok I actually thought about this a fair bit a few days ago and I think I have a good answer for this.
You’ve probably heard of the cheap bar trick that goes something like: “And what does a cow drink? Milk!”.
Irrespective of intelligence, humans tend to make silly cognitive errors like this because we are fundamentally pattern marchers.
In order to become a forerunner in a field, you necessarily have to be good at abstract pattern matching.
What happens as you age is that you no longer have the need to question assumptions because you know what’s real and what’s not. There’s also the decrease of white matter and an increase of grey matter which doesn’t help this.
As time goes on, certain assumptions change, essentially deprecating certain chunks of your crystallized learnings.
Some chunks of your thinking are still valid, so when you think something can be done, it most likely can be done.
However, if something falls outside your crystallized learning, you get a strong sense it’s wrong, when it might be because of your outdated assumptions.
You can try to hotswap the assumptions you have, but it becomes like Jenga the more years of experience you have in your field.
You either have to start from scratch and rebuild your lifetimes worth of learnings from the ground up or be super careful in reassessing everything you know