If you did not have an employment contract or agreement, you were an employee at will. An employee at will may be fired at any time, for any reason whatsoever. There is no need to share with the employee all the different reasons for which he could be fired, or all the policies, violation of which could result in termination; instead, if the employee does something which the employer disapproves of, they may simply terminate him. Also, an employer cannot anticipate every possible violation or problem; for example, it may reasonably not have occured to anyone that an employee would let a customer into the office and shut the door to the office.