Ask HN: Share a gem. Teach me and you.

One of my favorite discussion threads of all time, on any forum, was "Teach me and you. Give a gem" on the Civfanatics forum. It wound up being 15 pages of insights on how to play Civilization IV well, and was really a wonderful, enjoyable, community building experience. Here was the first post: "Share a "one-liner" simple strategy that can help beginners, seasoned players and maybe even be a gem that one of the pros can learn from. Feel free to explain your tip, but avoid complex, in-depth strategy." So, care to share a gem about technology, entrepreneurship, or general Hacker News type topics?