Ok, let's put it this way.. imagine that last May I wanted to buy 10 Trezor (I imagine you're familiar with it and I don't need to explain), their price was (??) 1 BTC each, therefore I needed 10 BTC which I didn't have. So I ask my friend Bob to lend me 10 BTC, with the agreement I will give him back 1BTC per month. Please note that when we did the agreement 1BTC=100USD (total debt 10BTC equivalent to 1000USD). Now, we are in December, I still owe my friend 4 BTC, but those 4 BTC equal almost 4000USD. Since I am buying those bitcoins each month when i receive my salary (if I had all the money at the beginning I wouldn't have ask my friend) my residual debt is now 4000USD, 4x my initial debt.

This is just in a short period, imagine this in 2 years time, with a longer time involved to pay back and a bigger amount involved. Solutions?