There are plenty of reasons why teamwork falls apart: poor communication, unclear expectations, lack of leadership … but more often than not, it comes down to reliability. No matter how professional, skilled, or charming you are, if people can’t depend on you to show up on time, do what you say, finish what you start, and say please and thank you, no one is going to want to work with you—and teamwork will grind to a halt. Here’s what you need to know.