In this case, the lesson was, don't protest against Israels policies. Israel has applied this lesson many times. There have been a lot of people killed and injured at these weekly protests. Sadly, they got an American girl or there would hardly be an issue. It seems that the protesters are not the only ones who have failed to learn their lesson. Israel has consistently failed to learn from their mistakes. Nobody hates admitting error more than the Israeli government. That is why they will feel obligated to continue causing casualties at the weekly protest, but they may be smart enough to avoid aiming at Americans for a while.
Netanyahu condemns West Bank arson attack, calling it 'terror' (Haaretz)
from the article: U.S. demands IDF probe how American lost eye at West Bank protest