What is the lowest rate of borrowing when a project doesn't make sense?

I mean, if you can't repay a minimal amount of interests, is the project even worth it?

it's a simple economic question, what do you think about it?

If a project can't make 1% or repayement per yer? 2%, 5%, 7? 25?

I mean a what rate you say : this is fucking crap?