You should NEVER rely on that theory that one punch in the right area will knock a man out. I don't know if you played any contact sports but there are many guys whose tolerance to take punishment is a lot higher than most.
In boxing, for example, there are guys who have what is called a "weak chin" or a "glass jaw". You hit them in a certain spot, they will go down. But you also have guys like MIKE TYSON, no matter where you hit him, he keeps coming. You soon realize he is your worst NIGHTMARE come true. All rules you thought applied to everyone is out the window. The only way to beat them is to out think them.
GEORGE FOREMAN was the same way. Muhammed Ali wrote in his autobiography that he was the real life BOOGIE MAN. In their fight in 1974, The Thriller in Manilla, he wrote how he threw everything he could at George in the early rounds but he kept coming at him, HARD. He hit him everywhere, it didn't matter.
So Ali started covering up and leaning back on the ropes, hoping George would wear himself out. He would make comments to George to get him mad so he would swing on him, "You hit like my mother" or "that didn't hurt punk, you can do better than that". This went on for 8 rounds, people even started booing Ali because it seemed like he was scared to fight George. Finally, in round 8, George had tried himself out from swinging on Ali. Ali hit him once and he went down for the count.
Marvalous Marvin Hagler, Aaron Pryor, etc. a female will not beat those guys, only another man could. You are not going to beat those kind of men with a lucky punch. There are many men out there who are like that, can take whatever you throw at them and keep coming.
Your absolute WORST NIGHTMARE standing in front of you.