Why Is The Foot-in-the-door Technique Effective?

Why Is The Foot-in-the-door Technique Effective? According to this explanation the foot-in-the-door is effective because: “compliance with a small request causes the subject to infer that he has a positive attitude toward cooperating with good causes; in turn, this positive attitude leads to compliance with the larger request” (Pliner, et al., 1974, p. 18). Why