Show HN: I built a live Bitcoin price aggregator with multiple indexes

But as a borrower, deflation blows. If I borrow 100 BTC and the terms of the loan are that I have to pay back 100 BTC + 10 BTC as interest, but the value of BTC has increased by another 10% I'm really paying 21% interest on the loan.

But as a borrower, inflation rocks. If I borrow 100 USD and the terms of the loan are that I have to pay back 100 USD + 10 USD as interest, but the value of USD has decreased by 10% I'm really paying 0% interest on the loan (actually, I might be able to beat inflation and come out ahead).

This goes back to what I mentioned in another thread [1] about buying and selling in either type of currency.

Let me hand wave some things, we'll assume that the real value of an item or ROI is static, and only the nominal value is changing with inflation or deflation.

Inflation: I borrow money to buy an item. I pay interest on the loan, and gain the benefit of having the item today rather than a year later when I would have saved up the cash. Over that year I pay off the loan, but with inflation I may get a discount of sorts on the item. If inflation is 10%, the nominal value is 10% higher the next year. If the interest payment is less than 10% I've saved money. If it's more than 10%, hopefully there was a profit in having the item now rather than later or I lost money.

Deflation: I borrow money to buy an item. I pay interest on the loan, and gain the benefit of having the item today rather than a year later when I would have saved up the cash. Over that year I pay off the loan, but with deflation I have an added cost. If deflation is 10%, the nominal value is 10% lower the next year. If the interest payment is negative ~10%, I've saved money. If it's higher, then hopefully there was a profit in having the item now rather than later or I lost money.

In fact, that matrix is essentially the same. Borrowers win in inflation (or might), while lenders might lose (but it beats leaving the cash under the mattress where it will lose value). Borrowers lose in deflation in most circumstances, while lenders win as long as borrowers don't default too often. Lenders under deflation have to be confident that the expected ROI of their loans will beat the deflation rate, or they might as well leave the cash alone. Lenders under inflation are virtually guaranteed that reasonable loan practices (subprime mortgages being an example of unreasonable loan practices) will be better than sitting on the cash if the economy is otherwise stable.

[1] https://news.ycombinator.com/item?id=6811101

That doesn't really answer the question. Grandparent wasn't asking "Why would you want to borrow BTC?". It was asking, "Why would you want to borrow in a deflationary currency such as BTC rather than a traditional, inflationary currency?"

As others have pointed out, the most obvious practical reason why a borrower might specifically desire a BTC-denominated loan is in order to short sell Bitcoin. For something like a business loan, it seems intuitive that choosing BTC over a traditional currency would accomplish little aside from maximizing the interest rate on your loan (in real terms). Admittedly there may be plenty of unwary buyers who'll happily enter into a loan like that without doing any math first - the entire payday/title loan industry is built on this fact - but an operation relying on that unfortunate fact doesn't jibe too well with the stated goal of behaving more ethically than the existing financial establishment. So hopefully there's something else to it?