Apart from obviously worrisome situations like a high fever or a non-responsive baby, you may want to reach out to a doctor if you see abnormal/unexpected behaviors in your 8-month-old baby. Such behaviors include if they have not started to crawl yet, if they always seem uninterested in playing, if they display a lack of appetite, and are being supremely fussy. There may be some underlying condition that needs to be treated. For the most part, however, be patient with your baby and understand that all babies have a different pace so do not compare your baby's development to the development pace of other babies.