Some fighting things that aren't said out loud.

 The common sense is that every attack creates some opening. Done correctly it's an opening your opponent cannot exploit, but it goes meta: it's impossible to always pick the unexploitable opening. To attack is to open a hole in your defence.

 You can defend perfectly, but doing so gives up any opportunity to attack. You have to stand too far away to initiate an attack they don't have time to respond to, precisely because you have to give yourself time to respond to all their attacks. You have to bunch up too much to riposte in a dangerous way. As you're standing back, they can carefully plan an attack that has no riposte.

 You win a fight when the opponent makes a mistake. If neither make a mistake, it is a draw.

 Not merely in martial arts. In a gunfight, you can put yourself in a pillbox without any windows, so you can't get shot, in exchange for being unable to shoot back.

 This generalizes to life. You can only win by giving Reality the opportunity to make you lose. If you can't lose, you don't prove anything. You can't gain anything at all.