From micro point of view, it is very natural to think that if everyone's net expense is less than their net income, they will get richer and richer and pay back the debt eventually
From macro point of view, in today's money based society, it is impossible. If the total amount of money at any given time frame is constant, one man's profit is always another one's loss, the net result of the whole nation will be zero (In fact negative, due to frictions in transactions and interests)
This is not true. You are confusing money amount and money flows. If the amount of money is constant, it is a conservative system in which a conservation law holds, and all fluxes balance.
Wealth is not the amount of money, but the utility that takes the opposite flow to the money flow.
If you have a cow, and I have 20 chicken, and you value my chicken more than your cow, and I value your cow more than my chicken, then we could exchange those, and both gain in utility. We could apply barter, or we could use money, or we could use debt.
If we use money, I first buy your cow, and with that money you buy my chicken. Money has flown, money is constant in amount, and we both won in utility (just as with a barter exchange).
The complex web of money flows does exactly the same.
Interest is nothing else but another money flow, of which both parties find an increase in utility by doing so.
If I borrow money to buy a house NOW, and I pay you back the money, with interest, then the only thing that happens is that there is a certain money flow from me to you (the interest) of which the utility for me is that I have my house NOW and not 20 years from now, which is to me much more useful than to have to live 20 years in a cardboard box while saving for my house. That money flow (the interest to you) is provided for by me working for an employer, who gives me a salary (another money flow) because he thinks that my working is more useful for him than the salary he provides me, and I'm happy with that salary because my time is worth less for me than the money I receive. My boss and I, we both win in utility. A part of that money flow to me goes into paying the interest to you, of which I also agreed that paying that interest is less costly to me than not having my house right now.
So we all win with these flows. If you use your money flow from me (the interest) to be a customer of my boss, and you pay my boss for some of the products he makes, the circle is closed, all money flows are conservative (that is, they respect a conservation law), and they are opposite to a service and goods flow that by itself is the result of a double increase in utility.
No money creation is necessary.