I think, like many fitness things, it's actually as much of a discipline thing as anything else.

When we're confronted with an escalator next to stairs, we take the escalator out of laziness, even though we wish we didn't.

But we'd actually prefer there not to be an escalator at all, so we'd have to walk.

Same thing as when you choose not to keep snacks at your desk because you know you'll eat them.

We prefer an environment that nudges us in the right direction, precisely because we don't always have the discipline we wish we had.