I only started to lean when I bought a share in my current steed last November. Didn't before that because I was sh1t scared of the engine even getting remotely near the point of quitting; even the slightest change in engine tone was not an enjoyable experience.
I know this is incorrect but wasn't taught during PPL, so didn't learn about it until later.
In fact the for the first 15 hours of my PPL training I thought the mixture control was just a way of shutting the engine down
Andy