Circuit breakers can trip for a few reasons. First is over current. That is where too much current is flowing through the circuit breaker, and the wire, and it trips itself off to protect the wiring from overheating and catching on fire.
Second is a short circuit. This can be a short to any opposing phase or to ground. The circuit breaker is again turning itself off to protect the wiring from a massive overload and burning hazard. If you reset a breaker and it trips, call Houston Electrician.com, we'll get there fast and fix it right."