This one ties in a bit I think with something yesterday. Craving is just another type of ignorance. Ignorance is the big one, craving is a specific one in which "we want, we want, we want". Now the word craving, in English we generally think it is part of desire, we want, but in the first two of the Four Noble Truths, Dukkha, the cause of Dukkha is our ignorance, craving, unwise reaction, the word that they use, the actual Pali, word is "Tanha", and Tanha strictly speaking does not mean craving in the English language. It is more of a thirst, a wanting, but it includes a wanting "to get rid of", also. So actually this means I want something, but also I want to get rid of something, I crave to get rid of that. Now, that is not normally the way that we use the word craving in English, but within Buddhism the root cause of our Dukkha is Tanha, which includes the wanting for something or the wanting to get rid of something, all based in ignorance as the root cause.