Complex sentence: A further factor in strenghthening commitment is suggested to be the norm of reciprocation: a person is expected to cooperate with individuals who do something for that person first and then later ask for a favor in return.
Split into simpler sentences: A further factor in strengthening commitment is suggested to be the norm of reciprocation. This is when a person is expected to cooperate with individuals who do something for them first and then later ask for a favour in return.