Tiny problems that are solved provide a common part that many people can be reasonably sure is free of bugs - if thousands of people use left-pad, you can be reasonably assured that it has no bugs (or else people wouldn't use it, or a bug report would be filed - "many eyes make all bugs shallow"), if a thousand people write left-pad, you will get many versions with bugs that are never found, because there is much higher entropy/surface area.