Most people will usually use the side of a bowl to help crack an egg in half. However, when doing so, tiny pieces of the egg shell can get mixed in with the egg itself and it can be a little difficult in removing the broken shells. A great tip in cracking an egg without getting egg shell mixed in is to crack the egg on a flat surface. Once the egg is cracked, place your thumb inside and split the egg shell.
Another good reason to use a flat surface is to eliminate any contamination that could get inside the egg once it is cracked.