Why Steem is Addicitive

I realised recently what makes Steem so addictive: It provides a natural variable reward schedule.

Basically, when writing a post, there is a possibility of a large reward, and those occur just often enough to keep us writing, and the unpredictability keeps us on our toes. The smaller rewards occur far more often, which also serves to reinforce our addiction.

Steem functions very similarly to a slot machine in terms of its reward schedule.

So, was this an intentional design aim, or did it happen by accident?