It's hard to remember to practice those platitudes day-to-day, which makes them worth repeating. You must register your predictions beforehand in order to avoid hindsight bias. You also have to avoid getting attached to them. Programmers very often commit map-v-territory mistakes, asserting how a thing works as if it were an observation of how it performs, and so on.
If all this is old hat to you, well, congrats! But it's not to everyone. And keep reading. It gets more practical after Ch 2 or 3.