I used to play a lot of video games as a kid. The games I played tended to become boring once I figured out all the patterns in it. The patterns could be as follows - do X and get Y points, do Z and get an extra life, etc.

When I didn't have any idea of all the patterns in the game, I would be very excited to play it. Because every time I did something, I received an unexpected reward. But once I had uncovered the patterns, obtaining the same rewards were less exciting.

This is why people buy lottery tickets, and listen to their music playlist on Shuffle. They contain unpredictable variable rewards.

All the social media applications (from LinkedIn to Tinder) make use of this. When you get that email notification from LinkedIn, it tells you that "10 people viewed your profile" or "this person sent you a message". They don't tell you in the email who these people were or what the message was, even though they know that is precisely what you'd like to know, more than the fact that that person sent you a message or ten people viewed your profile. The message might just be "Hey" and nothing else, or it could be an important request for a referral or some other question/information that you were looking forward to hear. You won't know what it is until you click on the notification and visit the website. Hence, clicking through represents an unpredictable variable reward. And this increases engagement and visits to the site.

Tinder works more or less on the same principle. Every time you swipe right, you don't know whether it will be a match or not, which is the unpredictable variable reward.

Donald Trump's election campaign was quite successful for this reason too. Every time he spoke at a rally or gave a television interview, you had no idea what he would say. Would he repeat the same stuff as before? Would he completely refute what he had said before and say the opposite? Would he say something altogether new? This kept people coming back to the television, which drove up the ratings for channels that covered him and they promptly covered him more as a result. Hillary, on the other hand, was more predictable. And hence, wasn't a big audience puller.

Sports draw huge audiences for the same reason.

If you are working on a product that you would like to be sticky with your audience and want them to come back again and again, this is the one feature that you have to provide.

On the flip side, if you want to focus on doing deep and meaningful work by avoiding distractions, if you want to write a blog post or work on your novel or your presentation for two hours in a row, you have to tame your mind to overcome its trigger-happy nature that makes it gravitate towards unpredictable variable rewards.