From a recent Numberphile video:
By the way, it’s always important to guess. Guessing is the way to learn and advance in science, both for students and researchers alike. If you guess right, you are very, very proud you got it right. If you guess wrong, you are really shocked; maybe not really, but slightly shocked, and that engages your thinking. You can learn what happened and then it makes you a little smarter next time. So always guess before solving any problem.
Source (6:05), edited for clarity
Setting hypotheses and testing them is one of the cornerstones of science and critical thinking. People practice it outside strict scientific fields too, but probably not as deliberately (the always part). After thinking about this for a couple of days, this struck me as odd because, as Professor Tadashi Tokieda had mentioned, it is an excellent learning method.
Guessing tests assumptions, reasoning, and knowing fundamentals. It can be used for more exact areas like programming and engineering, but also for messier situations like usability testing or sales meetings. The tricky part is remembering to stop for a few seconds, step back, and ask: “What do I expect to happen, and why?”