Laskern, the Aruch haShulchan says (OC 242:44) that is only if someone has a business where the natural order of things is for there to be ups and downs. However, if someone has a fixed income he should not. In fact, someone who borrows not knowing how he will not be able to repay is a rasha (Rambam Hilchot Malveh v’Loveh 1:3) and according to the Rav Soloveichik in the name of the Brisker Rav he is a thief.
JJ, suppose Hashem decides that if you will work a certain amount you will earn a certain amount?