> "Everything is variable reward. Is everything gambling?"

well, no. If you work overtime and get paid overtime, you are not gambling and that is not a variable reward.

Humans engage more with rewards that are intermittent and variable. Like Futurama's scene from 'The Scary Door' where the character says "A casino where I'm winning, I must be in heaven! A casino where I always win, that's boring, I must really be IN HELL!". A constant predictable reward is boring, less engaging. So if you know you get no overtime, but sometimes your boss rewards you with $5 coffee voucher, sometimes a free pizza dinner, sometimes double-time pay for the time worked or a half-day off, now you might be gambling 1hr overtime for an intermittent variable reward.

> "Drive to work, traffic might be good or might be bad."

Good traffic is not a "reward" for driving to work(!) and you have to drive to work regardless so you are not risking anything [you might be risking your life, but you are not making a choice which can reward you with good traffic]. You might say that going a different route is a choice and a gamble which could reward you with good traffic, but traffic engineering does not work that way because if there was a consistently low-traffic route, everyone else would take that route until it was no faster than any other route. Traffic will generally be the predictable and similar every day, plus 'arriving at work early' is not much of a reward.