Self love

Will Self, putting it nicely:

while you can know a man by what turns him on, you can only really understand him by what turns him off.

There's something very true here; and perhaps it could even go a step further. What you can know a man is that he can be turned on, assuming he can; or to put it another way, you can best know a man by understanding whether the-turn-on or the-turn-off is the defaulty against which his psychic economy struggles to balance itself.