Do you see a symmetry of products vs. money? Both are assets that some people need and some other want to give. If one is in deflation, then another is in inflation to another. Why don't you buy MacBook 2 years from now, when it'll cost the same, but will be more awesome? Because you have non-infinite "time preference": you want certain things today vs. tomorrow.
Why people want to hold money? Because it gives them ability to spend it anytime on anything - it's most liquid, most desirable commodity. This is big value in having something in your wallet - freedom to make decisions in face of future uncertainty. If you can freely choose between money which loses in value and money which doesn't, which one every person would put their savings in? Then, everyone spends according to his own time preference - amount of desire to enjoy stuff today vs. tomorrow.
http://blog.oleganza.com/post/43378777734/on-circulation-of-...
Here's also a thought experiment on deflationary spiral: http://blog.oleganza.com/post/66215430631/deflationary-spira...