The simplest explanation of inflation I've ever read comes from a story about cigarettes and prisoners.
It's written by @yanisvaroufakis and it perfectly describes why inflation hurts savers.
Here's a story about a prisoner-of-war camp...
1/ Periodically, the Red Cross would place a few more cigarettes in the prisoners’ packages but keep the quantity of chocolate, tea, and coffee the same.
When extra cigarettes arrived, each cigarette now bought less coffee, less chocolate, and less tea.
Why?
2/ Since a larger number of cigs now corresponded to the same amount of coffee/tea, each individual cigarette corresponded to less coffee/less tea.
The opposite also held true:
The fewer cigs the Red Cross placed, the greater the exchange value (purchasing power) of each cig.