Any trigger, be it a text message notification or an emotion, prompts a user to take some action, like opening the app or clicking a button. 
This simple action can be internalized and make the users click on the app icon to open it even if there isn’t any new message.

The Action

... deployed by the messaging software and many other products is composed of:
<ol>
<li>Trigger</li>
<li>Action</li>
<li>Variable Reward</li>
<li>Investment</li>
</ol>
Understanding these four steps makes us see the hidden psychology behind a user's daily tech habits.

The Four-Step Hook

The technological tools we use keeps us connected to the people that matter to us, and the text (later rich text message) is one of the oldest ways of communication since portable phones came into existence. 
It also has a hidden secret that makes us keep checking it.

The Message

Phones became smart more than a decade ago and started doing almost everything.
While the app store has millions of apps to take care of our needs, connecting with other people remains one of the few fundamental uses of the phone.
Actual phone call usage has gone down drastically, while services like text messages, video calls, email, and rich messages (Facebook Messenger and Whatsapp) are used almost throughout the day.

Smartphones and Messaging

... towards doing something can be external, like a ‘click here’ button, or internal, like an emotion or craving. A successful trigger graduates from being an external one into something inbuilt in the user.
Example: One feels lonely or bored and instinctively opens Facebook.
Text messages have the notification as an external trigger when you get a new message from a friend, giving you a small rush in the head.

The Trigger

<ul>
<li>BF Skinner, a psychologist, found that if an action gives a variable, unpredictable reward, it is more frequently used and is addictive.</li>
<li>Like a slot machine, the reward is not something that the user knows beforehand, providing a sense of wonder, intrigue and mystery.</li>
<li>In the case of messages, the variability is baked in the message itself, and different apps utilize novel ways to keep the user hooked.</li>
</ul>

Variable Reward

There is a push provided to the user to ‘invest’ in the service so that there are variable rewards in the future. This can be anything from uploading a new profile picture to set a status update for all to see. 
The investment increases the probability of the next trigger happening, as in the case of messages when a message is sent, the likelihood of a reply increases manifold.

Investment

In this post, I analyze he psychology behind how messaging services like WhatsApp utilize the Hook Model to keep users engaged and coming back.