Why does Israel always act with restraint against the terrorists?

This question was asked on Little Green Footballs, and I'm sure it's a question that many of you are thinking about: I know many here don't put much weight in polls, but for the last ten years, poll after poll has shown that the American public is overwhelmingly in support of Israel. Do the Israelis know this? Because if they do learn this, maybe it would help strengthen them to do what they have