system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it that when you cut a small part of plastic it makes tearing much easier?
gpt
Making a cut produces a focus point that will have to absorb all of your applied stress, rather than spreading it more evenly across the entire surface.

The plastic is strong enough in bulk to absorb your strength, but not strong enough to stop all that force applied to a single spot.