"Something I've repeatedly found useful is that when debugging and you have a conjecture, not only look for evidence that a correlation/causation is present; but also look for evidence that it isn't."

In my opinion, the absolute, utter core essence of science can be expressed simply as "Always be trying to prove yourself wrong." The human brain is extremely biased in the other direction, and it's darned good at proving itself correct. It can prove itself correct in absurdly powerful ways. Always be fighting it, always be looking for ways to prove yourself wrong. If you do it seriously, things like "the scientific method" will naturally fall out of your serious attempts and need not be surrounded by near-worship, whereas no amount of worshipfully-following a checklist of the "scientific method" without the true effort to prove yourself wrong will produce truth; the human brain is far more powerful than the "scientific method" or any such static methodology.

I have deliberately left the word 'theory' out of this post. This scientific mindset beyond that into engineering and any number of day-to-day activities.