What was the most confidence building moment for you as a programmer?

Most of us have started learning programming by fiddling with an editor and the language syntax. Those who continue to find joy in the process then goes on to build more stuff with it. This is analogous to using a chisel and hammer to carve out wood. First we learn to hold the chisel and hammer properly (similar to learning syntax). Only then can we carve out designs on wood (building substantial programs, small or large).

But there comes a moment where after practising quite some time, a switch gets flipped inside our head and we start to see the tools we use (chisel or programming language) as an all powerful tool whose use is limited only by our imagination. We become so sure of our skill with the tool that it becomes almost second nature to us. We imagine new things that we can build and use our tools like butter.

In programming this confidence building moment may come at different times for different people. For me it came after learning in deep about programming languages from Essentials of Programming Languages book: https://en.wikipedia.org/wiki/Essentials_of_Programming_Languages. It was a moment of euphoria for me.

Later on I got a similar moment from studying CS:aPP: https://csapp.cs.cmu.edu/. But it was not as intense.

What was yours?