Egg whites will not become foamy or stiff if there is one single trace of egg yolk mixed in with them. Therefore, break your eggs with care.
If, by accident, a small bit of yolk falls into the whites, try to scoop it out with HALF A BROKEN EGGSHELL. If the yolk is smeared on the side of a mixing bowl, wipe it off with a clean cloth.
If, by chance, a small bit of eggshell falls into a batch of egg whites or yolks or a mixture of both, it is easy to remove it, again, with HALF A BROKEN EGGSHELL.