Measure Twice
There’s an old saying in the building trade (a trade that I’m utterly unfamiliar with, whose work often approximates black magic to this Grumpy Metal Guy) - Measure twice, cut once. The further into my professional career I get, the more I’m convinced that this applies not just to physical tasks, but software related tasks as well.
In software terms, this saying is (roughly) translated to Quantify Everything. Statistics are the best tool in our arsenal to determine how well something is performing, how efficient our people and processes are, and how to compare two things in a non-subjective sense.