This is true if the reason to leave was something else than money to start with. If someone asks a raise because he feels like he's not getting paid what he's w

This is true if the reason to leave was something else than money to start with. If someone asks a raise because he feels like he's not getting paid what he's worth, giving a raise will definitely help him stay. Or, if he has regular raises, he'll be less likely to get in the "why am I not paid my worth" mentality. Typically I've seen companies paying high salaries for newly hired senior developers because the market was favorable, but not giving raises to developers hired in a less favorable time or acquired seniority internally. Those are typically people who left because of money (and rightly so). It's funny, it feels like this is the kind of thinking that pushes managers to make the wrong decision and refuse a raise to a deserving employee.