Why is it important to perform multiple trials in an experiment -- meaning that you include many test individuals or samples?

What impact might an economic downturn have on a borrower’s fixed-rate mortgage? a. it might cause a borrower’s payments to go up. b. it might cause a borrower’s payments to go down. c. it has no impact because a fixed-rate mortgage cannot change. d. it has no impact because the economy does not affect interest rates.