I'm still amazed at how many managers will unwittingly play head games with people who work for them.  Notice I said unwittingly. 

Most managers don't want to confuse or stress out their employees.  They want to be helpful.  So, when they have an employee who might need a light touch the manager might soft peddle.  There might be subtle suggestions and hints here and there so as to not hurt the employee's feelings, but to the detriment of execution.  Over time the manager might not see enough progress.  The manager could overcompensate because she thought the issues had been addressed with the employee.  Now you have a mad manager and a confused/hurt employee.

As managers we should always tell an employee what the real deal is as clearly as possible.  It is when we misuse the art of management to push harder or softer than truly necessary is when we get in trouble.  Just be straight up with people without being too cold and we'll all have a better day at work.