column "tum_first_name" of relation "tbl_users" does not exist, even when it does

I have a tbl_users, where there are a few columns like TUM_First_Name,TUM_Last_Name and so on. However, when I try an insert query, an error says :- column "tum_first_name" of relation "tbl_users" does not exist Here is a photo of the schema :- Update :- Surprisingly, after I renamed all the column names to lower cases, and called this same query, it worked. So, when my table had new column names as tum_first_name,tum_last_name, etc., running the query INSERT INTO tbl_users(TUM_First_Name,TUM_Last_Name,)... worked fine What is this ambiguity ?