system
Given the following post, respond as if you're commenting on Reddit:
human
Why is it that for some things (like pulling the seal off a milk bottle), you need dry fingers or rough textures, but for other things (like opening a plastic carrier bag) you need wet fingers and smooth textures?

Why do two seemingly similar surfaces need such different approaches to generate grip?
gpt
When you are separating two similar surfaces which are not fixed(hard surfaces), there is cohesive force between the surfaces and you need wet fingers but when you need to pull something slippery off of hard surface, you need rough textures to counter the adhesive force between the surfaces. Example of the former can be counting currency notes.