Why do media users constantly "just check" their email, social media and other online services throughout the day? They never know when new media messages will have arrived; it's the power of intermittent reinforcement.

The allure is that a really great social media message is posted on average of every $4$ minutes, so it's important to check often.

They never know when new media messages will mean a check is in the mail.

Media users are addicted to the online services that make their lives more convenient.