It means to assume that something is normal and/or correct. If we go out to dinner every night, and I always pay, and you never thank me, you are "taking me for granted." If we go out again and you don't get out your wallet, you are "taking it for granted" that I will pay (because I always have).

The most common use of “take for granted” does have a negative connotation, that of lack of appreciation. But in the Descartes example it just means to “accept without thinking about it”. That’s not necessarily negative. I want my children to take (it) for granted that I love them. (I don’t want them to have doubt or to have to think about it) I don’t want my children to take (it) for granted that I will give them money every time they want it. (That would be a negative trait for them to have)

Hi Dinghui, To take something or someone for granted means to not appreciate or to not take into consideration their values. Hope this helps!