A mitt just taken out of the wrapper will probably be uncomfortable to use, due to the fact that the material from which it has been made has not reached the level of flexibility required for optimal comfort. In short, it will be quite stiff. Softening the material and putting it through use, then, is called "breaking" the glove. This is primarily done through repeatedly catching baseballs, and it can take anything from several days to whole weeks. To keep it simple, the more you use your mitt, the better it's going to perform.