system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why are jar lids smooth and round as opposed to an easier to grip shape?
gpt
Cost, standardising the shape makes it cheap, if a product decides to use a non standard shape the set up cost will be huge. 

Ideally a nobble around the perimeter of the lid like a tyre track would help but it isn't going to happen .

If you struggle try inserting the handle of a spoon or blunt table knife under the rim and lever a little bit,  there will be a little pop when you let air inside the jar and it will then open easily.