system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does wetting your finger create extra grip when opening a plastic bag or picking up a piece of paper?

I always thought dry surfaces would have more grip compared to wet surfaces. Like athletes using chalk.
gpt
It's because water sticks to things in ways that aren't friction based.

When you put chalk on your hand, you're increasing the friction between you and say the climbing wall you're on. Friction only works under compression, so any time you need to pull or slide past, it doesn't really work.

When you put water on your finger, it sticks to both you, and the plastic bag. This stickiness is better in shear forces (sliding past) and tension. Not great mind you, but better than pure friction. 

If it doesn't stick to the thing you're up against, then it doesn't give any extra grip. That's why ceramic tile floors and rocks are slippery, the water would much rather stick to you and itself than the ceramic.