You have 6 types of glands that make 3 components of tears:

Lacrimal glands, Krause glands and Wolfring glands make the water part

Zeiss and meibomian make the oil

Goblet cells make the mucous part

They're all important but they get worse as you age. Artifical tears are a great product, but like most medicines can be ruined by the process of producing them. As many comments have mentioned, generics can occasionally be an issue with contamination whereas brand names in the US all have better quality controls.