It's part of the wisdom of confessing to a priest that we find it far more embarrassing to reveal our sins to another human being than we do to admit them to God. The sting is far greater! It shouldn't be, of course — obviously we should be far more abashed in front of God, in prayer — but human nature works that way.
Perhaps the lack of confessing to a human being robs Protestants -- and "progressive" Catholics, who scoff at individual confession -- of an important motivator in resisting sin. After all, if you know that if you do the sin, you have to admit it to another person to get right with God, that's uncomfortable, and the thought of having to do that just might provide the strength to resist the temptation.