1. Eggs are infertile.
2. Eggs are cracked and contents dried out.
3. Eggs are too old when set.
4. Eggs are held in extreme temperatures prior to incubation.
5. Shells are contaminated.
6. Eggs are not turned often enough.
7. Temperature is too high, too low or too variable.
8. Too little humidity or too much humidity in the incubator.
9. Improper ventilation.