Deflationary thinking meant everyone expects prices to be lower tomorrow, so no one spent money on needed items and simply waited to make purchases to save money. This slowed down the economy into a death spiral that they still are climbing out of. Mortgages became crushing. You can't get a raise. Interest and deflation work together to make debt nearly inescapable.
The point of money is to be spent, i.e. facilitate the simple transfer of value. An excellent example of the direct damaging effects of deflation is bitcoin. No one spends it. It has utterly failed at its goal to become a primary mechanism to transfer value. Everyone expects its value to keep increasing so it is almost never transferred (to the point that hodling and never spending became a meme). Slowing down the exchange of money is what kills an economy.
