I believe Commitment - Consistency Theory is best represented in a children’s book If You Give a Mouse a Cookie by Laura Joffe Numeroff. Giving the mouse a cookie encourages the mouse to ask for a glass of milk and many requests follow that. Similarly, agreeing to sign a petition may result in e-mails that request donations or further involvement and interaction. “Freedman and Fraser’s (1966) seminal work found that compliance with a small initial request positively influenced compliance with a larger, related, subsequent request (Vaidyanathan & Aggarwal, 2005, pp. 234)."

Use caution when giving your valuable time and energy. A commitment can be an isolated event; it is ok to say “no”.
Joffe Numeroff, L. (1985). If you give a mouse a cookie. New York: Harpers Collins Publishers.
Vaidyanathan, R. & Aggarwal, P. (2005). Using commitments to drive consistency: Enhancing the effectiveness of cause-related marketing communications. Journal of Marketing Communications, 11(4), 231-246.