Legitimizing paltry contributions, also known as single penny tactic, is a useful influence technique for softening people’s hearts when soliciting charitable contributions, and it may work with other kinds of requests. Its essence is to present your request as minimal, non-threatening, small as a pixel.
In a seminal study on this technique by Robert Cialdini and David Schroeder, published in 1976, the experimenters went door to door soliciting donations on behalf of the American Cancer Society. 
- Some people heard a standard request, which led about 30% of the people to donate some money.
- Other people heard a similar pitch only with the minimizing language: “even a penny will help.” Now, more than 50% of the people opened their wallet. Interestingly, the amounts were not that different.
This technique works by putting the heat on people’s ego: anyone can find a few spare pennies, so if they don’t you give anything, it makes them look cheap. So this technique takes away justifications such as “I don’t have enough money.” This image-maintenance mechanism explains why this technique works when donations are requested on the spot, but not when people are asked to mail in their contributions—when there is no social pressure from other people, people don’t have to worry about their image. 
Additional reason why this technique may increase compliance is that it makes the request seem non-threatening and easy to perform, and the easier something is to perform, the more compliance it gets.
- Robert B. Cialdini and David A. Schroeder, Increasing Compliance by Legitimizing Paltry Contributions: When Even a Penny Helps, Journal of Personality and Social Psychology,34, 599–604 (1976).
- Robert A. Reeves, Ruthann M. Macolini, and Roy C. Martin, Legitimizing Paltry Contributions: On-the-spot vs. Mail-in Requests, Journal of Applied Social Psychology, 17, 731–738 (1987).