I bought a house on a mortgage. If its price changes later, how will it affect the ease of repaying the loan? I had some difficulty in understanding this paragraph in an article explaining the movie, 'The Big Short':


  Most of us when buying a house take out a loan (mortgage) and pay back
  the purchase price over time. We also usually hope that the value of
  the house we buy will go up not down. In the US, many people had
  come to assume that house prices would always rise, because they’d
  risen without fail for many years. This attitude saw mortgage lenders
  offering riskier and riskier loans to people who’d only be able to
  make payments if the price of their house continued to increase.


https://www.ecnmy.org/engage/the-big-short/
If a mortaged house decreases its market price after the mortage was made, the bank is in risk in case of default - it might be unable to recover the amount it loaned. In practice this doesn't change the amount you owe to the bank or the monthly payment -  you owe the same regardless of the value of the house after making the mortage. 

I believe the author meant that the people the banks were lending to would only be able to afford to pay the mortages if the economy kept on booming, and they would remain employed.