Does everyone follow 40X rent rule?

[Freeman Schultz]

I have been talking to a bunch of landlords about the rule that applicants must have an income that is at least  40x the monthly rent. Some of them are complete  sticklers to that rule. But other landlords leave a little wiggle room.  I know one landlord who will let it slide if their income goes past 50%. For example, if the rent is 2500 and the applicant has an income of $60,000, this landlord will rent the apartment out to that tenant. What do you all think of that rule?