There are a lot of people who claim to understand complex subjects, but disagree with each other about them. Sometimes, it is a matter of caring about different priorities or values, especially in politics, but to a lesser extent almost everywhere. Modern engineering really began when Thomas Young realized that when he walked on a bouncy surface, it had to deflect noticeably to support his weight, but every surface also had to deflect to support every weight, just not enough to see easily. Everything is a spring, but most engineers still try to think in terms of rigid and flexible parts, and get a lot of trouble over the variations that they ignore. I have a better than average understanding of several engineering principles, but still struggle with other branches, let alone the rest of the library.