"The ability to engage in executive inhibition or conscious self-restraint has arisen so as to decouple events from potential responses, interrupt the automatic flow of stimulus–response behaving, and provide for an opportunity to choose potential courses of action.
As a consequence of the former capacities, the value assigned to a delayed consequence has been increased (its reward value is not as steeply discounted as before). This leads to a motivational shift in the individual’s preference of delayed rewards over immediate ones (from a higher to a lower time preference in economic terms). The individual is now increasing the subjective use-value of a delayed goal and is therefore more motivated by the prospect (mental contemplation) of such a goal.
The capacity to self-direct speech and language provides the individual a means of using symbolic representations as a form of rule-governed behavior opening them up to all of the advantages that self-speech provides as noted above. Though such rules are necessarily simple, specific, and concrete in early development, with maturation there arises a capacity to guide behavior by longer, more complex, and more abstract rules. ...
The level of behavioral complexity needed here has increased by the added stage of the self-direction of actions. Behavior is no longer simple, automatic, and short-lived; it is now delayed, more complex, and deliberate. Alternative courses of action are being contemplated and are considered over a longer duration, giving rise to a need for a greater complexity of behavior so as to serve as the means to the goal and to bridge the delay in time to get it. ..."