Diabetics lack the ability to make their own insulin, in type 1. They have trouble because when someone can not break down their own glucose, there becomes too much of it in their body which can cause a number of problems. If a normal person's blood sugar gets low our body produces glycogen which gets broken down into glucose which our body will then bring into the cells raising our blood glucose. A diabetic needs to eat something to get those glucose molecules into their body, but then they run into another problem. If they don't have insulin, the body cant take up the glucose, so they have to balance the amount of glucose with the amount of insulin to stay healthy. Sorry this is so long... :)