Why is it said that staying in a single room is best for one person?

There are too many things to consider when it comes to sharing a rental, as one can only take care of their own emotional state. However, the same cannot be said for roommates. It's unfortunate to encounter roommates who are greasy or messy, but what's even worse is dealing with those who have bad habits. It can be extremely challenging. [Disappointed face] It can be a matter of life and death.