How do I hand-roll homemade pasta made with egg?
Pasta dough has to be sufficiently moist to be rolled properly.

Rolling the pasta (in a pasta machine) aligns the gluten strands so they stretch out and become parallel to each other. If the dough is too dry, it is more difficult to align them. This is why it's a good idea to coat unused dough in a thin coating of oil and cling wrap if you're not immediately working with it (a damp tea towel over the bowl will work as well).