Sometimes it can feel like reading the code should be the last resort. That feeling is wrong. It is a dangerous feeling, bred from discomfort.
Reading the code isn’t always comfortable. It can feel like an arduous chore, especially if it isn’t a core habit of yours.
The code is truth. The only complete truth. If physicists had all the source code for the universe, how many experiments do you think they would run? My guess is zero.
Read the code and all else will follow. Do you wonder how something works? Read the code. Are you stuck on understanding an internal service? Read their code. Are you debugging how a coworkers’ library works? Read the code.
Always read the code.