Sooner or later most people sacrifice defense for punch. Or positioning for punch. If you do either of those, you stand a very good chance of getting knocked out. I remember when I was a kid I had a neighbor who would get drunk on Sundays and do yardwork (he had a hot wife he could have been inside banging, but hey...let's lay down some mulch!). One time after he finished he asked me how it looked, and it looked fine except for the empty beer bottles every 3-4 feet. Our other neighbor said: "Yeah Dave works in circles. He works hard all day and doesn't get shit done."
A lot of fighters work in circles. They work very hard to do something that doesn't accomplish their goal. When they do this they leave openings themselves and can be unprepared to handle the response. A good example of this in boxing was Bert Cooper against Michael Moorer, round 1:
Juan Manuel Marquez also had a habit of knocking out people who knocked him DOWN, and tried to go for the kill. I remember telling my students that if I ever trained anyone to fight Marquez I would say DON'T knock him down, statistically you almost guarantee you'll be knocked out by him. Unless you're Floyd Mayweather Jr. or Manny Pacquiao. And don't go right to him and force a fight. In fact, do as little as possible. Tim Bradley "beat" him that way.