B. f. skinner was a behaviorist; as such he would argue that the most important things that shape development are:

B.F. skinner was a behaviorist; as such he would argue that the most important things that shape development are "Rewards and punishments".
Reward and punishment are two sides of a similar coin. They are the two types of extraneous inspiration, which can be fairly noxious in the way it seems to work at the time. In conditioning, punishment stops activity while reward energizes it.