From my experience, doing heel hooks is more about how much you know, more so than what they know... A common misconception I have heard in the jiu jitsu community is that "the heel hook is too dangerous because the person you are doing it to wont feel pain until the knee is already damaged", and that CAN BE correct depending on HOW you are doing the technique. There are ways you can do the heel hook so they feel pain in their foot/ankle/and eventually the knee, so they tap before any real damage occurs.. Also I have found that you have to leave your ego at the door when it comes to heel hooks, for example, if you have a heel hook tight, and they're a noob (who is not tapping), just let it go.. Same if they try to spin out of it.. they go to spin the wrong way.. let go! that is where most (again in my experience) heel hook related injuries occur..