As a developer, I spend quite a bit of time typing. Typing code, typing email responses to clients and recruiters, typing jokes in Slack.
As a child, I was fortunate enough to have access to a computer at home and the internet. Our computer was not fancy enough though to play any of the games the other kids were playing, like Starcraft or Counter Strike, so I spent quite a bit of time playing text-based games instead. No need for graphics cards when all your computer needs to do is show text scrolling by. No need for a fast internet connection even. Playing these games involved so much typing I could not help but get faster. I had no formal typing training, so my methods were far from conventional, but they worked.
Years later I read articles like Why You Should Use a Mechanical Keyboard and bought a fancy new mechanical keyboard, one small enough to carry around even.
I thought it might finally be time to learn to type properly, so I looked around and found typing.com and started working to correct years of habit. It took about 4 weeks of fairly regular practice to finally train myself again. I still sometimes forget and revert back to my old ways, especially when I want to quickly whip up some code to show something to a student.
For record-keeping purposes, I even recorded a little video to compare before and after my training. You can see before I mostly only used my middle finger on my left hand and didn't use my pinky-fingers on either hand.
Another convenient side-effect of typing properly is that I put less force into each keystroke which helps to make my keyboard quieter also. Hooray!