The way I've seen it happen is this: you have some developers, some are good, some are not that good. The good developers leave, the bad stay. In time that bad

The way I've seen it happen is this: you have some developers, some are good, some are not that good. The good developers leave, the bad stay. In time that bad developer will be the only one on the team that has 10 years experience. It will be the only person that knows all the little details of your project and so he will even get a management position, or a senior title. Of course, all those details should be documented somewhere but they are not.