A very satisfactory debugging happened to me not long ago, when I discovered that assignement in C++ and Python doesn't work exactly the same.. I never took courses in Python so I had no way of knowing. I'm a self taught programmer, so I also always feel a bit insecure about my skills.
What made it really satisfying was that when I finally googled it, it was only to confirm the "diagnosis" that I had already made. I felt like years of struggles got me somewhere, now I feel a bit less insecure about my knowledge and skills in programming. :)