I can turn out most parts clean and to spec without breaking a sweat now. But hand me something with a tolerance so tight there's almost no room for error, all tricky angles and fine finishes, and I start sweating the setup. The everyday work is mine; the really precise, complicated stuff still beats me.
More people experience this than they realize.
You can machine ordinary parts well, but the complex, tight-tolerance work still defeats you.
If this sounds familiar, the Library can help you find the bigger picture.