Source: Magnum Force.
Lesson: pretty self-explanatory. Every person needs to know their limitations. Either you will find them out through life experience or training or self-examination, or you will have your limitations demonstrated to you, perhaps fatally.
This was the first Rule that came full blown from just one line in a movie. Harry Callahan used it to mock the bad cop Briggs, who had once used the line to try to tell Harry that he was outmatched.
This rule has many applications. For instance, there are physical limits to how much activity we can endure, or how well we can shoot, or how much money we can spend. There are also limits to what we are willing to do, for a number of reasons. There are moral limits to what a person is willing to do, too.
For me, this means I have to train so I know what I’m capable of doing physically. Many people think that when the time comes, they will “rise to the occasion.” But experience shows that we will actually regress to our level of training. So we must always be advancing our ability through training and practice.
It also means I need to have well thought out rules of engagement, that lay out what I will do in certain situations. No one should wait until an encounter to decide how they will act. This is especially true of self defense situations.
More on rules of engagement later.