[greatreorx]

"But both doesn't mean time discounting is something irrational."

It's over-discounting that's irrational.

If I have a school paper due in a month, the probability that I won't have to do the paper is certainly non-zero (I could die, my professor could get sick, etc)... but it's likely something less than a .01% chance that an event like that will happen. It's not rational to put off a paper until the last couple days if there's still a 99.99% chance you will have to turn it in. I over value my current reward of being able to watch more TV now, while under discounting the future cost of having to do the paper in the future. I treat it more like there's a 10%+ chance that I won't actually have to do the paper.