I would argue that shame is often the reason people keep things that they are ashamed of secret so that no one ever knows about them. People can be deeply ashamed of things about themselves even when this perception is not reinforced by others who are aware.

For example, you might be ashamed of being a coward, a homosexual, having a birth defect, or any number of things that don't require you to do anything or for anyone to know those things about you. Typically, though, guilt is about something you did that you wish you hadn't, particularly if it negatively affected others.

It's also quite possible to feel guilt and shame simultaneously if you, for instance, fail to come to someone's aid because you are afraid, and then that person suffers because of your inaction.