Why would you do a thing you didn't ultimately want to do though?
Regrettably I need money in order to eat food.
So you don't become weak and overweight, for instance.
When future-you wishes present-you had done the thing. So in a sense there is a you (future-you) that actually does want to do the thing.
This isn't that they don't want to do it, they do, but they don't want the effort involved.
Necessity. I don’t want to do my taxes every year and I need to force myself to just sit down and do it.
how to do something when your mind wanna do it because it's rational but your emotions don't because it's painful
Yes! This is the real question.
I wrote about this (as a tangent, but anyway) recently. https://asemic-horizon.com/2025/07/28/julian/
TL;DR "akrasia", procrastination etc. are all forms of ambivalence that are not nearly as "psychological" and individual as usually presented. The nausea is in the world itself.
Many reasons. Maybe not doing that thing will be bad inthe long run. Maybe you want the fruit of doing that thing, but cannot enjoy doing it right now, etc.
A popular example would be sports if you're not very fit. You would obviously have tangible health benefits if you did it, you may look more attractive, you may have more energy both physically and mentally. But since you're a couch potatoe sports is demanding, exhausting and sucks. Would you do more sports it would suck less or you might even find it enjoyable, but you don't and that's where you are.
This puts you in the weird spot of wanting a thing but not wanting to do what would get you there, even if the reasons you don't want to do it would vanish if you did it.
You can only really overcome this mentally, e.g. by priming yourself in certain ways, or by creating situations where you don't have a choice, because others rely on you, etc.
At the end of the day I don't think there is such a thing. If you do I think deep down you want to do it, otherwise you wouldn't.
I read this as: how you can motivate yourself to do something you're currently not motivated to do but "ultimately" believe is worth doing.