Here's the problem. We don't create good incentives for new runners. We say something like "Try running 30 minutes a day." But time is not a good incentive to work harder. Distance is. I think we should recommend that the new runner jog/run 3 miles a day. Because if we tell people to run for 30 minutes, they'll slowly jog it every day. No incentive to work harder. But, if it's 3 miles, then the sooner they get there, the sooner they're done.
Now, I know what you're thinking. But then eventually, their workouts will shrink from 45 to 30 minutes. But, guess what? They're still burning more calories running 3 miles in 30 minutes than running 3 miles in 45 minutes!
Diet and exercise are all mental, and I feel like we're not incentivizing people appropriately to beat the mental aspect of the game.