How can credit be both asset as well as a dept trap?

People can borrow money from banks at the time of need and then return the money with required interest when they have benefitted from the money borrowed.
But sometimes , especially poor farmers , even after taking loans from banks suffer unexpected loss when crop failure occurs or natural disaster takes place.....in these conditions they are unable to repay the loan and the they take another loan to repay that loan. In this way they fall into a debt trap which is very troubling situation.
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