As a kid I accidently plugged a mic into the speaker port and was surprised that, when I put my ear close to the mic, I could hear the computer sounds! It made sense in hindsight, and since then I knew they are kind of functionally equivalent.

My first “electric guitar” as a kid was my acoustic with an earphone taped to the bridge and plugged to the mic in of my boom box.

It was also my first “fuzz pedal” because the sound never came out clean :)