All nouns in Spanish require a gender article (el/la or los/las). In English, you do not have to figure out whether "día" should be prefixed with el or la -- and in the case of "día" despite it ending in "a" which usually implies feminine and la, it's actually masculine and is properly "el día."

That doesn't even bring into it examples like ellos/ellas ("they" or "them" in English) referring to a male group or a female group where the standard rule is to use ellos if referring to an unknown group or even a group of 100 women and one man, the only application of ellas should be when you can verify every single member of the group is female.