It's not about under-performance. You are taking the 'boss knows best' stance which anyone who has ever held a job knows is utterly incorrect. People who manage corporations are usually very immature and have child-like sensibilities. They may decide that they simply don't like someone, that a person is the wrong race or gender, or they want to try and scare other employees. There is no second chance in office politics. Any sort of "second chance" notice indicates a loss of respect and is grounds for immediate firing of my boss. Employees should keep a resignation letter at their desk and be continuously looking for their next job unless they are absolutely sure they are not working under the typical psycopathic boss or founder.