Assuming you're working on regular software where you can run it in isolation, without cost, I disagree with "don't guess".
A guess might be your best opportunity to test a theory about a bug you don't understand. That's particularly true where you're a newcomer to an area and the documentation is written for someone with different experience.
A series of guesses and tests can narrow down the problem, and ultimately help you fix a bug on your own terms, a bit like tracer fire.
I much _prefer_ to build a mental model, and to spot the bug as a deviation from that model. And unguided guesswork can be a sign that you're flailing. But guessing can be a strategy to build that model.
In my book that's not a guess, but a hypthesis, which is indeed a great way to narrow down the problem space. What I meant was to avoid blind guessing in the hope of striking luck, which comes back to haunt us most of the time.
A guess might be your best opportunity to test a theory about a bug you don't understand. That's particularly true where you're a newcomer to an area and the documentation is written for someone with different experience.
A series of guesses and tests can narrow down the problem, and ultimately help you fix a bug on your own terms, a bit like tracer fire.
I much _prefer_ to build a mental model, and to spot the bug as a deviation from that model. And unguided guesswork can be a sign that you're flailing. But guessing can be a strategy to build that model.