Working on nighttime sleep isn't exactly easy, but daytime sleep requires action. At bedtime, both sleep pressure (or sleep drive) and your baby's circadian rhythm (their biological clock) are pushing them to sleep. But during the day, only sleep pressure is present—and your baby can overcome it and fight to stay awake. However, naps play an important role in baby's sleep overall. If your baby isn't a great napper, chances are she'll be overtired at bedtime and will have continued sleep problems, which is why getting into a good nap schedule is crucial.