My research on common reasons that few, or no, chicks hatch: 1. Eggs are infertile, old, or improperly handled before hatch. 2. Temperatures are too low, too high, or unstable during hatch. 3. Humidity levels are too high or too low. 4. Eggs are not turned often enough. 5. Incubator opened while chicks are hatching. I set 6 eggs 5 hatched I may never know exactly what caused one not to hatch. However, I did an eggtopsy to get a better understanding of what happened to no avail fully formed no deformities not shrink wrapped. • All eggs were fertile the oldest was 7 days old they were handle carefully and stored in egg carton pointed end down at 65° F. • Ambient temperature was 99.5º F. in a forced air incubator from day 1 to day 22. • The chick was fully formed, and zipped 3/4 the shell, the humidity and temperature were fine because 83% hatched. • Eggs were turned by auto egg turner for 18 days then lock down procedure was followed including raising the humidity to 71% and held there until hatch was complete. I kept a log of temperature and humidity daily and all was OK according to what I have read. Once again I had a 83% hatch rate but would like to know where I went wrong. Why did my 6th egg not hatch? Edited to add: Five eggs were blue they all hatched, one egg was brown it zipped 3/4 but did not hatch. The same rooster fertilized all 6 eggs.