How do people find bugs?

See How do people find bugs? on cryptologie.net

Ian Miers once said something like that: “you need time, expertise, and meaningful engagement”.

Meaningful engagement can lead to meaningful bugs, and meaningful bugs can be found at different levels. So you’re here, seating in your undies in the dark, with a beer on your side and some uber eats lying on the floor. Your computer is staring back at you, blinking at a frequency you can’t notice, and waiting for you to find a bug in this protocol. What do you do?

This post goes over the ways in which you can find hard bugs. David suggests going through proofs or formal verification. I doubt these things are needed in front end development, but I would like to understand how these things work. Proving programs is something that I’ve seen floated around quite a lot these days.