Let us say that the apples are grown year round. There are no fridges, so apples can only be stored for a few days before rotting.
One day the newspapers publish an (accurate) prediction that the apple crops will take a marked downturn in a few months time because of an expected weather event, perhaps el-nino or some such. Everyone will now want to "save" so that they don't go hungry. They can not store up apples because they will rot, so instead they all want to buy jewels so they can "sell" (exchange) them for apples at a later date. The jewel/apple exchange rate will rise dramatically. People will see the high jewel/apple ratio and assume that they have lots of savings. Later on the harvest fails and there is a shortage of apples. People will now be forced to start selling their jewels for apples. The jewel/apple exchange rate will plummet. The amount of apples people can buy with their jewels will be disappointing.
Here is a diagram of the situation (click on it to show full size):
Now in the real world the jewels may be a variety of savings vehicles, shares/bonds/money. Unfortunately things are complicated by the fact that the amount of money in the system is variable (due to the magic of fractional reserve banking) but one way or another, in the real world, our current savings are liable to disappoint. Either through defaults, monetary inflation or even both.
