" In recent years behavioral scientists have shed some light on why these waiting techniques can be powerful. Let’s first look at the notion that texting back right away makes you less appealing. Psychologists have conducted hundreds of studies in which they reward lab animals in different ways under different conditions. One of the most intriguing findings is that “reward uncertainty”—in which, for instance, animals cannot predict whether pushing a lever will get them food—can dramatically increase their interest in getting a reward, while also enhancing their dopamine levels so that they basically feel coked up.
If a text back from someone is considered a “reward,” consider the fact that lab animals who get rewarded for pushing a lever every time will eventually slow down because they know that the next time they want a reward, it will be waiting for them. So basically, if you are the guy or girl who texts back immediately, you are taken for granted and ultimately lower your value as a reward. As a result, the person doesn’t feel as much of an urge to text you or, in the case of the lab animal, push the lever. "

― Aziz Ansari