  Friendship is a fundamental characteristic of human beings and usually
assumed to be reciprocal in nature. Despite this common expectation, in
reality, not all friendships by default are reciprocal nor created equal. Here,
we show that reciprocated friendships are more intimate and they are
substantially different from those that are not. We examine the role of
reciprocal ties in inducing more effective peer pressure in a cooperative
arrangements setting and find that the directionality of friendship ties can
significantly limit the ability to persuade others to act. Specifically, we
observe a higher behavioral change and more effective peer-influence when
subjects shared reciprocal ties with their peers compared to sharing unilateral
ones. Moreover, through spreading process simulation, we find that although
unilateral ties diffuse behaviors across communities, reciprocal ties play more
important role at the early stages of the diffusion process.
