And the more you have done to express your commitment, and the more public you have made your commitment, the more resistant you are to changing your mind about it.
For example, in one experiment, researchers went around in a neighborhood and asked people if they would be willing to put a three-inch square sign in their window that said "Be a safe driver."
Two weeks later a different volunteer went through the same neighborhood and asked for something outrageous: "Would you be willing to put a billboard on your lawn supporting driver safety?"
Those who had earlier agreed to the little sign were much more likely to say yes to the billboard than people who had refused the little sign. And almost everyone who they asked to put the billboard on their front lawn who had not been asked to display the little sign refused.
In other words, once someone committed themselves a little bit to the cause by putting the little sign in their window, they were more committed to the cause. They were more willing to do something about it. This is the principle of commitment and consistency.
The author, Robert Cialdini, defined the principle this way:
"It is, quite simply, our nearly obsessive desire to be (and to appear) consistent with what we have already done. Once we have made a choice or taken a stand, we will encounter personal and interpersonal pressures to behave consistently with that commitment. Those pressures will cause us to respond in ways that justify our earlier decision."
So when you can get someone to sign a petition to stop Saudis from teaching hatred in American schools or to stop imams from preaching jihad in American mosques, the person who signs it commits herself a little to the cause.
It is a small act. It only takes a few moments. But signing a petition makes her more committed to the cause in general. She may begin to think of herself as an advocate for the cause. She will be more likely to commit to something bigger for the cause in the future when an opportunity arises.