https://en.wikipedia.org/wiki/Causes_of_the_Great_Depression
Deflation or Hyperinflation on the other side is nothing compared to the crises we have today.
They are both a path for disaster, this is the primary fear of economists.
Good explanation: https://www.quora.com/Why-is-2-the-ideal-inflation-rate
-- Federal Reserve Bank of Minneapolis (Research Department)
What do you do?
1) Spend the least amount of money today that you can to continue living and put the rest under your mattress?
2) Anything else.
Being rational, you choose one. Now magnify this by every other rational actor in the area affected by deflation.
You can no longer buy bread because the grocer decided not to spend his money on new stocks. You no longer have a job because your employer would rather have your wages than your work. The widget factory expansion gets canceled because no one will loan the company money to pay for it.