You don't know how many people your life is connected to until you do something that lets everyone down. When we screw-up we see most clearly (if we're willing to look) how we are tied to others. Very few people live in such complete isolation that their choices have no effect on someone else.
I once heard Pastor John Ortberg describe how he uses his journal to write down as many of the negative consequences he can think of if he were to choose to give in to a temptation facing him. I think that's a great exercise and I wish I used it more often. Stopping to think about how our choices affect others can act as a deterrent to errant behavior.