system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can large loans (e.g. mortgages) be structured so that your first several payments are mostly interest and little principal?

Is there a better reason than, "Because they can"? It seems so unfair to the borrower.
gpt
Loans do not have to be structured that way; that's just the result of homeowner's desire to have a stable payment for the life of the loan. 

If your payment is fixed, some of it must be allocated to interest and some to principle. Early in the loan the principle is large, so the interest is large, and the interest has to be paid every year (this is what you're paying the bank to have the loan). As a result, once you pay the interest, there isn't much left over for paying principle.

Over time, as the principle shrinks, the interest gets smaller but your payment is the same size, so more goes to principle.

If you don't have fixed size payments, you can do whatever you like after you pay the interest. You can structure a loan so that you pay the same amount of principle on every payment, but then your total payment will be much larger early on when the interest is also large (many home equity line-of-credit loans can be paid this way).