I started programming at ~8 and as a kid you often are sure the compiler is wrong, and it never is. (maybe once, have a vague memory of it)

Then years later I started playing with Nim when it was still in beta, I think I found 3 compiler bugs in a few weeks! Reported them all, all got fixed!

And then a few years later found a bug in LLVM, doing weird stuff with Rust and SIMD intrinsics. Was difficult to even communicate what was going wrong but did get it reported and confirmed eventually!