I have to eat specific amount of fiber to go

I have to eat specific amounts of fiber to be able to go one day and not the other, that is, 25 grams of fiber a day, including chia seeds (which I think do the main part of the job). If I exceed, like, 35-40 grams of fiber a day (my body is used to it; I've always eaten a lot of fiber), I get blocked, and there's no way to unblock me except by stuffing myself with laxatives... but whyyyyy. Everyone I know goes even if they eat two rice cakes and a little chicken breast a day 😔