A scar is, at its best, a badge of honor and, at its worst, a ongoing reminder of what not to do. In either case, a scar is a permenant record of an experience, and more importantly an experience significant enough to draw blood. I don't possess a single scar that I acquired intentionally, which is why I consider my scars to be more signicant than any tattoo.
A scar is a record of an action, a tattoo is, at best, a record of an idea.
If I record a short list of scars and associated lessons that I possess, I end up with something like this.
The use of a knife while paying no attention to knife safety ought to be avoided. I once accidentally stabbed myself in the hand while absent mindedly cutting the ring from a water-bottle.
Drunk people do not enjoy friendly debate - the scars resulting from a stab wound on my arm and leg testify to this.
Climbing a cedar tree ought to be avoided. The scar memorializing the time I was impaled by a branch as I fell from a tree reminds me of this constantly.
The unarmed hand should be kept out of the line of action in fencing. The many small scars on said hand that I have acquired as a fencer have slowly taught me this.
I am not qualified to repair generators. The scar that resulted when I was nearly electrocuted and, in a moment of surprise, drove a small bolt through my elbow taught me this.
If your mother tells you NOT to climb on the monkey bars when she was not around, you should not, at the first opportunity, climb on the monkey bars when she is not around.
If you're going to get into a fight, one might want to protect one's face - a thin scar above my eye reminds me of this.
I have a great many other scars, most of which probably have associated lessons as well, but they are less interesting.