If people expect deflation then they will defer buying things because their money will buy more in the future than it will right now. This should reduce aggrega

If people expect deflation then they will defer buying things because their money will buy more in the future than it will right now. This should reduce aggregate demand and also feedback on itself as falling demand should put further downward pressure on prices, causing more deflation. It sounds nice if you are only a buyer but almost everyone in the economy is both a buyer and a seller. Beyond that it's an issue for investors. Interest rates have a nominal lower bound at 0% (because you can always just hold money instead of lending it) so the minimum real interest rate becomes effectively the rate of deflation. So imagine that deflation is 4% and I have a use of capital with a real rate of return of 3%. It won't get funded because investors can achieve a higher real return (4%) by just sitting on capital instead of investing it.