Helpful. But this mental model can be improved. A McDonald's meal is an expense. A mobile device, you can argue, is an investment. The device can return dail

Helpful. But this mental model can be improved. A McDonald's meal is an expense. A mobile device, you can argue, is an investment. The device can return daily joy*. A meal is, special events with friends aside, a soon forgotten one-off. * The device can also be a distraction and a time-suck. That needs to be factored in.