My question is why someone should borrow a POS token?
To stake it and give them back later.
The question is, if staking or borrowing will cost or give more.
Or the price of POS! You exchange your POS to $ before lending and you have to change it back to POS after lending. When you lend 100 days and at the day of start lending POS is worth 1$ and at the day of end lending POS is worth 10$ you lost a lot of money, because you borrowed instead of holding. If POS is worth only 10 Cents at the day of end lending you win a a lot of money
