Sure. The book is a sort of resource for learning the programming language Scheme, where the authors will present an illustrative piece of code and discuss different aspects of its behavior in the form of a question-and-answer dialogue with the reader.

In this case, the authors are discussing how to perform numerical comparisons using only a simple set of basic procedures, and they've come up with a method that has a subtle error. The lines above encourage the reader to figure out if and why it's an error.

With computers, it's really easy to just have a half-baked idea, twiddle some bits, and watch things change, but sometimes the surface appearance of a change is not the whole story. Remembering to "think first, then try" helps me maintain the right discipline for really understanding what's going on in complex systems. Thinking first about my mental model of a situation prompts questions like this:

• Does my model explain the whole thing?
• What would I expect to see if my model is accurate? Can I verify that I see those things?
• Does my model make useful predictions about future behavior? Can I test that now, or make sure that when it happens, I gather the data I need to confirm it?

It's harder psychologically (and maybe too late) to ask those questions in retrospect if you try first, and then think, and if you skip asking them, then you'll suffer later.