* Psi Operatives learn/unlock new abilities by training in the Psi Lab instead of experience on the battlefield. A Psi Operative's skills are learned in a randomized fashion, with players given a choice between three randomly selected skills to unlock each time a Psi Operative is trained. Unlike other classes, Psi Operatives are capable of unlocking all of their abilities, but only through a significant expenditure in time and resources. (Source xcom wiki)