How do you remember all the results when reading a textbook?

When reading a math textbook each chapter usually has 1-3 major theorems and definitions which are easy to remember because of how big of a result they usually are. But in addition to these major theorems there are also a handful of smaller theorems, lemmas, and corollaries that are needed to do the exercises. How do you manage to remember them? I always find myself flipping back to the chapter when doing exercises and over time this helps me remember the result but after moving on from the chapter I tend to forget them again. Is this to be expected or is this a sign of weak understanding?