Did you not hear this expression when somebody said, I am resigning? Especially, from your boss when you told him you are quitting. The typical response is 'Why?', 'I am shocked to hear this', 'I never expected, that "you" would do this', etc etc. BULL SHIT!!
If I were a team leader, I exactly know who is reporting to me, what is the work being carried out, what are individual aspirations, what is the value addition to each team member and how each person is peforming. Even if a small disconnect between individual's expectation from the organization and his/her aspiration ignites the negative thinking. I fully support the theory that people quit not from the organization, but from their immediate boss.
And to enlighten the poor boss's soul, the chicken starts to think at the first negative sign and many things keep adding up. Finally the individual either encounters a spike that completely demotivates him/her or reaches a saturation state accumulating all the encounters in the past (like illogical appraisal talks etc). This process could take anytime from 6 months to one year. And then the employee announces his decision to be free from the boss (not from the organization). So my dear bosses, when somebody says I want to resign, please dont pretend to put a shocking expression on your face. You better be aware of whats happening in your team and atleast verify where the 'disconnect' is. Mere talking does not help, act.