Do not take to heart all the things that people say, lest you hear your servant cursing you. Your heart knows that many times you yourself have cursed others. (ESV)The first sentence seems like a very obvious bit of advice that one might pick up anywhere in the world, perhaps even on Pinterest or Facebook. Don't take everything to heart, or you'll hear your servant cursing you. Don't absorb all that's said, because sometimes people say things that aren't all that swell.
However, our line of reasoning to follow that up would likely be something along the lines of, "they don't know you", "they can't understand you", "they're too narrow-minded", or perhaps, most profoundly, "haters gonna hate".
Solomon takes a different tact. He says, "Your heart knows that many times you yourself have cursed others." Whoa. I see two main implications here. First, don't absorb every careless word, because you know that your own words are often careless. Second, cut others some slack. They haven't committed any offense against you that you haven't done to someone else--maybe even to them! Either way we take this (I think both are legitimate), the point is surprising: he points the finger back at us. It's not, "ignore them, they suck." Rather, it is, "don't take it all to heart; if you do, you're a hypocrite."