We spend a large part of our life trying to persuade others to do something.
Improving your ability to persuade can yield huge benefits over a lifetime. It also doesn't hurt to be able to realize when others are using psychology to try and persuate you.
Persuading someone using consistency is about them not you.
When you try to persuade someone and you consider the principle of consistency as a means to do so you need to think about the other person. What have they said in the past? What have they done in the past? What are their personal beliefs? If you know the answer to one or more of those questions and can align your request with those answers you stand a much better chance of hearing them say “Yes!”
Here’s an example. In sales we talk about an “up front close” as a way of making more sales. As a salesperson, if I do a good job asking questions and listening then it’s very likely a prospective customer will tell me exactly what I need to do to earn their business. But it’s not enough to just hear them because I need to use this new understanding in conjunction with the principle of consistency to increase my chances of earning their business. To do this I might say something like, “If we can get the car in the color you want, with the DVD player and matching floor mats at the price we’ve been discussing, will you buy the car from us?” If the customer has told you exactly what they want and the price they need, and you can meet all the criteria then it’s only logical that they would answer your question saying, “If you can do all that I’ll buy the car from you.” But the key is asking them because once someone says they’ll do something they feel their own internal pressure to live up to their word.