I ran into this a while back too. Most of the time, it happens when you’re modifying a slice of a DataFrame instead of the original DataFrame, so pandas isn’t sure whether you’re changing the original data or just a copy. Using .loc[] for assignments usually fixes it. If you’re intentionally working with a subset, creating an explicit .copy() before making changes also helps avoid the warning. It’s one of those pandas messages that’s worth understanding early because it can prevent some tricky bugs later.