An addition to the idea that The Hero Leads is the rule that says: The bad guy must be as bad as possible.

In many a well-told movie, the hero and the bad guy are very often two halves of the same person struggling for supremacy, and for that reason are almost equal in power and ability.

The point is that the hero and the bad guy are a matched set and should be of equal skill and strength, with the bad guy being just slightly more powerful than the hero because he is willing to go to any lengths to win. After all, the bad guy has given up on having “family values” by definition. This does not mean you make the bad guy impossible to beat — just a challenge that looks impossible.