Troubleshooting and Signal Flow.
The key to be a good audio engineer and figure out fast any problem you face or a troubleshooting, whether you work in a studio production, live sound or any field related to audio engineer you must know how your signal flows.

It is a must to know how the signal runs in every consul or mixer you use. There are a lot of things to check if any problem happened. For example, if you plugged in a microphone in the stage box and not getting any signal try to make a list in your mind why there is no signal. check if the connectors are connected properly from the stage box to the mixer. check the microphone pre amp. After that, check the inputs and outputs setup in your daw you're using. After that you start looking and figuring out if any level is turned down on the mixer or something. Same thing goes for headphones. Honestly, same procedures applies to any problem you face. Keep in mind to brain Storm the problem quickly In order organize your thoughts and solve it properly.