Generally, the body is programmed to sleep best overnight and to be most alert during the day and early evening. If you work different shifts throughout the day it may be more difficult to get enough sleep. For example, if you start work late in the evening, it could result in having difficulty sleeping when coming back home with the noise and light of the daytime. When working very early shifts or ones late in the evening, workers often complain of being tired, both on and off the job. It may be harder to concentrate and be alert while at work.