Human nature is a funny thing.
We all like to think of ourselves as ethical and professional. However, those words have very different meanings to each individual.
Think about it. How many times just in the last few weeks have you: broken an appointment; done something you know is bad for you; cut some corner because no one would really know; or violated a commitment just because it wasn't convenient?
We will rationalize and justify to ourselves why this was acceptable all day long. This helps us get through the day believing we are still "professional" and "ethical" even when we violate our own standards, much less anyone else's. Our own ethical systems are malleable, bending to the pressures of the situation.
Here's an article I wrote a few years ago that illustrates this in action. It's a short parable. But it shows the tendency for people to change the rules of the game, after the fact, when it suits them. This is especially true when we make promises while in the middle of a challenging situation.
We're all human. But, if we want to be truly ethical and professional we should only make promises we intend to keep and then keep them.