nitty - gritty usually means fine details - gritty refers to grit such as dirt in tight corners, not exactly sure what nitty refers to. but the word nitty gritty can be seen as looking at dirt in tight corners. this is used as a metaphor to being very through in examining things. to the point of paranoid.

Nitty gritty can mean "basic" for example in a sentence " let's get to the nitty gritty of the contract" it really means let's get to the basic information.