house hacking + mortgage requirements

[Sang Nguyen]

Hey gang!

I'm curious if someone can shed some light for me. I recently talked to a lender (Wells Fargo) and told them that I was looking to buy a multifamily, live in 1 unit, and rent out the others. They told me that a 3 or 4 unit will require at least 20% down. They also said that I needed 6 or 7 months of PITI, even though I'll be living in it. Did I tell them the wrong thing?

The reason for this post is because, if I'm buying a property, and I can easily afford to mortgage, why is the PITI requirement even a thing?