How long do you have? Hungry, alone, disturbed by a sound, cold, too hot, bed lumpy, needing to toilet ...
However, please don't leave him or her to cry.
We now know that leaving our dogs to suffer distress can cause damage to the brain similar to PTSD in humans – this means the dog will be more likely to be more anxious, nervous, fearful in the future. There is nothing positive to come out of leaving a distressed animal to cry it out.
If you had a child who was crying in the night time, you would comfort and reassure them, please do the same for your dog. Can he or she sleep in the same room as you for a while (it doesn't have to be forever) until he or she is settled?