“Don’t forget, if he paid for the whole thing in full, then the money he spent is merely what you have to pay in interest. That is to say, he didn’t spend 500K less than you. You spent 1.3 million more than him.”
So basically, if OP had gotten a 1.3 million 30-year mortgage, then just the interest he would have to pay on that mortgage would add up to 800K. He would end up having to pay back 2.1 million. So if the friend was able to pay for the unit in full, 800K up front, then he didn't get the unit for 500K cheaper, he got it for 1.3 million cheaper than OP.
“Don’t forget, if he paid for the whole thing in full, then the money he spent is merely what you have to pay in interest. That is to say, he didn’t spend 500K less than you. You spent 1.3 million more than him.”
Huh?
So basically, if OP had gotten a 1.3 million 30-year mortgage, then just the interest he would have to pay on that mortgage would add up to 800K. He would end up having to pay back 2.1 million. So if the friend was able to pay for the unit in full, 800K up front, then he didn't get the unit for 500K cheaper, he got it for 1.3 million cheaper than OP.
Oh right, I forgot that most people get mortgages. But why does he think the other person paid up front while OP got a mortgage?
I think he just wrote about it that way because he knew it would be maximally upsetting to think about for OP