Could you keep an affair secret?

I asked why do people feel a need to confess? Now I want to know if you think you could keep an affair a secret if you had to.

I will stipulate to everyone that no one would ever have an affair, so none of you would need to keep that secret. However, if you ever found a compelling reason to keep such a secret, could you actually do it, or would you be unable to keep from confessing? Why?