The problem starts with either loans coming with high interest rates, making it difficult to meet up the demand, or the most common issue is spending that borrowed money on things that can't be accounted for and having no plan of repayment being laid
That is one of the biggest reasons why countries, firms, and even individuals tend to have debt all their lives because they don't have a repayment plan nor do they have a plan about how they are going to use the money they are borrowing so that it can provide them some benefit. Suppose you are an individual, and you keep borrowing money for personal expenditures without a proper income source. In that case, you are going to get in trouble when the time of repayment comes because you won't be able to repay the loans.
Bad loans become burdens very quickly. This is why it is said that it is not everyone's cup of tea to be able to manage loans and lent finances properly; it requires a lot of critical thinking and planning, and everyone can't do it. You will end up paying interest for your lifetime if you take a loan and can't repay it on time.