Why do babies fight sleep? First, babies aren't born knowing the value of a good night's sleep and they lack maturity. The 3 main reasons babies fight sleep are over-tiredness, under-tiredness, and separation anxiety. In today's article, we explain 3 reasons your baby might be fighting sleep and 5 things you can try today to help! Baby Fighting Sleep? 3 Reasons Why There are 3 primary reasons why most babies fight sleep at bedtime and nap time: Baby is Overtired This is hands-down