Guys, calm down, Elwar is being sarcastic, he's obviously playing on the whole "Deflationary currencies are doomed because no one spends money that will be worth more in the future" concept by applying it to fiat money and showing how it doesn't hold water.
I'm not sure it is a good comparison. If you are lending your money the borrower generally isn't putting it under the mattress but instead is spending the funds and economic activity results. So lending is essentially the same as spending.
Now there are differing beliefs as to which is better ... spending today by the borrower versus later spending that would occur by you (from your bitcoins kept "under the mattress"). Let's say the borrower uses the funds to buy a car for commuting to work, whereas your later spending might be used to import some expensive bottles of wine to add to your collection in your wine cellar, let's say. For the economy as a whole that money might be more useful going to the car today rather than to the wine for the cellar later. And thus you lending out the money is better than you buying gold with it and sticking it in the ground, for instance -- at least that's the argument as I understand it.
However, the problem is that the lending isn't just going for the cars for commuters and other productive uses but instead it goes for overpaying for goods and services and for speculation on commodities such as crude oil which raises the street price for all. So there's good lending (investment) and bad lending (resulting in malinvestment). Evidence of systemic malinvestment might look like this
Unemployment worsening in much of Europe:
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http://www.cbc.ca/news/interactives/map-europe-unemployment/while at the exact same time a designer handbag manufacturer sees sales in Europe double for the quarter:
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http://www.foxbusiness.com/industries/2013/05/29/michael-kors-net-income-doubles-in-4qi.e., lots of money sloshing around, going to consumption spending instead of to uses that increase productivity, or to factories, etc. If there's more profit from creating designer handbags than, let's say, designing and improving water purification technology, then that's where human talent will focus their efforts. If markets are left alone they are pretty good about figuring out the where and when investment should occur.
But there are those who think the central bank is smarter than you as far as what you should be doing with your money, and monetary policy is used to persuade you to behave in a certain way. Like spending it now (to cause economic activity) versus seeing it lose value (as the result of currency inflation).