It is the laying of a :"clutch" that gradually brings on the broody hormones, so leaving an egg is is wasteful of an egg that you might rather have for breakfast. Some hens lay a clutch of 30eggs or more--how wasteful to leave those eggs in a nest (but a hen who steals a nest hidden outside, may lay that many! And few hens can not cover that many eggs when they do set , so less are likely to hatch.) However, it is usually pullets that lay that many eggs before setting, and older hens will lay fewer--like 10-15 before setting, so leaving eggs in the nest --better false eggs, while not "making" them become broody, will have you thinking that is why she is now setting. A good broody will set on an empty nest, when her clutch is finished---even if you gather her egg every day that she lays--when Mother Nature says SET--she SETS!. However, what ever works for you--that is good! But, Make a hen go broody, you cannot, only Mother Nature (with the individual hen) determines it! A good broody is a real treasure!