system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did a piece of leather sharpen an olde timey razor when leather is softer than steel?
gpt
The purpose of the leather isn't to "sharpen" it's to "hone". 

In the first stage of getting dull the tip of the razor will bend. The leather strop is used to 'push' the tip back into the right alignment without removing any material. This process is called "honing", you should do it a lot, which is why you don't acutally want to use something hard that will remove material (you'd actually wear out the knife from loss of material).   
  
If the knife becomes very dull then you start to do actual damage to the edge, and then you need to remove material to make a new edge. That process is called "sharpening".