That was, I believe, implicit in the original post. The reason that it's scary is that it doesn't just apply to scratching a rash, it also applies to doing hard drugs.

Reference points, as used by default, make it very easy to throw your life away. That's what makes it scary.

"Jam now" is a necessary condition, not a sufficient one.

first hour or day

If I decide to, say, learn Spanish, then I expect every hour spent on the task, including the first one, to pay a perceptible return.