"A very long time. Or a reeeally short one, if you look at how old the universe is," Tim said with a smile. "You can offer to shake hands with anyone. Most people do it when they meet someone for the first time. Some do it every time they meet the person or sometimes as a goodbye, but not often. When you meet someone you've never met or when you make a deal, those are the two times that you want to make sure to shake their hand. It's polite with gravitas - it makes something official and important.