I thought this was interesting. This is actually very true. One of the key factors to Slack’s success is that their product is “sticky” or habit forming. They actually have a method behind that called the Hook Cycle. http://www.nirandfar.com/2014/11/slack.html
It explains how Slack taps into the neuroscience behind people’s dependencies to search for rewards of the tribe, hunt and self. Most products that can offer a variable reward system like Slack, will likely have more success with user adoption and retention.