Trust.

If there is one thing that takes an eternity to build up, and can be diminished within a heartbeat, it is trust. I bring this up because people don't realize how important it is. Be it from picking good friends, significant other, etc. So many people will say things like "I will always got your back", but when you really need them to hold you down, they're often MIA. I guess this is just another way to weed out the snakes, right?