I think it is important to know what our bodies are really asking for when we have cravings.... both in general, and when we are making big changes like changing what we eat (like a starter 30 day Paleo challenge).
When I think about it, what makes sense to me is that our bodies know what it needs (nutrient/vitamin/mineral) and can only "ask" us for it in terms of craving foods that it knows we've eaten that contain it. They may not be the best sources, but it's what we've eaten.
For example, we shouldn't feel guilty for craving chocolate if what that translates to is our body asking for magnesium. Alternative sources of magnesium include (amongst others) fruits like bananas and avocados.
Toss the guilt and frustration by searching online for "what your food cravings really mean", or check out some of the sites that I have referred to: