1) Unless you had a written employment contract, you were an employee at will, and an employee at will, as the term implies, may be terminated at any time, even within 4 days of starting. (If you had a written employment contract, you could only be terminated in accordance with the contract's terms.)2) The law deos not require any amount of training before saying that someone is unfit for a job, or any chance for the employee to prove him/herself; the employer can tell him/her as he/she is walking in the door for the first time that "we changed our mind; you're not fit for the job and are terminated." That is part of being an employee at will; you may be fired not just at any time, but for any reason.