I would tell my friend that bananas have a growing season. This means that when the bananas are ready to be harvested the market will soon be saturated with bananas. This means the prices of bananas will start to come down because there are more bananas than there are shoppers for them. But when the season is done or a hurricane hits an area where the bananas are grown then there supply of bananas goes down and stores will start having a hard time keeping them in stock. This means that the price will slowly start to climb because people will be willing to pay more for the same bananas just so they can have them.