Relationships are a testing ground. You are measured as a professional, and as a person, by your willingness to follow through on your commitments. Trying is not enough, good intentions are not enough, excuses are not enough.
The only thing that matters, after all is said and done, is that you did what you said you would do. There is no more powerful way to build trust, solidify relationships and separate yourself from the competition.
Commitment? doing what you say you will long after the mood has taken you.
Yoda said it best "There is no try, only do, or do not."