Why is $1,000 in five years worth less than $1,000 today?

inflation

Explanation:

As a country prints more money the buying power of the money decreases because their is simply more of it. It's like apples, the more apples in a community the less valuable each individual apple becomes because they are less rare than the year before, same goes for the amount of money in a country. The more money in a country, the less valuable it is because it is no longer as rare.

the answer is not negative reinforcement.