In my personal experience, the debris that were causing me to flat in the past were not those foreign objects that were stuck on the tire and puncturing the tube. It's those metal shards that look like foil and they move around the wheel depending on the gravity. They do look like tin foils and they're very small, maybe no more than 2mm, but when you feel them with your fingers they're quite sharp. Now this specific debris can't just be easily located if you're doing a shortcut with your repair 'coz they move around.

Everybody has their own experiences with their flats. I'm just sharing mine.