<prompt> Human: Popular advice here is to get a mortgage with low interest rate 4 and invest the cash you would have in the market which would likely yield at least 6 which will outperform the mortgage interest. My question is: why do banks hand out these massive mortgages and getting 4 back on their return, rather than investing their own money in the market?  <response>: Originating mortgages generates a lot of fee based revenue for banks. 