Measurement is tricky

What we all want is a simple, reliable, objective measurement of the "real" adhesion of our system.

Unfortunately there is no such thing as "real" adhesion. Everything depends on everything else. Which is why the cartoon doesn't even know which way to pull! The point of the Testing section is to show how each of the "standard" techniques for measuring adhesion is full of issues and artefacts. With exactly the same materials tested in three different ways peel, lap and butt you get three very different answers. And what is obviously a pure shear test, the Lap Joint turns out to be mostly peel when it fails.