I couldn't even feel the Modafinil on day 3 without taking 5x the dose. That's a bit silly.

Instant release amphetamine ends up being more like a party drug for the same reason, though less extreme.

Compare that to a slow release amphetamine (prodrug) like Vyvanse where most people can hit a 2+ week cycle of constant use, or an indefinite cycle by only dosing a fraction of the week.