For what it's worth, in Design and Evolution of C++, Stroustrup says that when he was designing features, he would often think of a simple rule that he couldn't

For what it's worth, in Design and Evolution of C++, Stroustrup says that when he was designing features, he would often think of a simple rule that he couldn't enforce (e.g., "couldn't enforce" being "if you violate this rule, the results are undefined") and a complex rule that he could enforce. He generally tried to pick the simpler, easier to teach rule. Unfortunately, that means there's more undefined behavior if those simpler rules are violated.