Sometimes we just face insurmountable obstacles regardless of our efforts.
There are a lot of things coming gradually throughout our career but we can't be good at everything.
Moreover, our experience naturally can't be evenly spread and some of our abilities are just better than others.
Being senior engineer means being good at solving tasks yet it doesn't necessarily mean being able to provide quality solutions. Think of it as of poetry. One can be a very literate person yet completely unable to see nor feel the difference between Shakespeare poetry and dross. Even more simple than that: imagine a person who can't see difference between "your work sucks" and "this result could be better under certain conditions". From my humble experience the thing that hurts me the most is OOP. Understanding OOP isn't easy. Being able to properly use it is a really tough task even for veteran developers.
The point I'm trying to make here is simple: there is always something that you're really bad at and clueless about. Stay open for the idea that you might be wrong. Be extra careful with it. You'll struggle to learn benefits of using hammer if you're a huge expert in using rock. Which doesn't mean that rock is better than hammer when it comes to nails.