If you have ever had someone betray your trust, then you know how important it is for you to be a trustworthy person.
Unfortunately, we see it happen all the time - public officials who mislead their constituents, bosses who lie to employees, employees who fail to do their job when no one is looking, or students and parents who take shortcuts in the educational system. In reality, trust may be an underlying issue in many of the world's problems.
If a person can't be trusted, it doesn't matter what they do or how they behave. There will always be a shadow of doubt about that person - at least to the person or the people they've betrayed.
On the other hand, people who are trustworthy don't take the easy way out. They are honest when telling the truth, which may mean tough consequences. They follow through on commitments - even when something more exciting may come along. They accept responsibility for what has gone wrong - even when no one would ever know they caused the problem.
Those are the kind of people we want in our lives - to lead us, to represent us, to employ us, and to befriend us.