Originally Posted by
Sixty Fiver
One flat is often caused by debris while a second and third might be the result of not finding the offending particulate that caused the first flat.
(...)
It is almost invisible to the eye and very hard to remove without fairly fine tweezers and is also easy to miss.
Exactly. That's been my experience too. Last time it was a tiny piece of wire, 1mm maybe, that I could not see without a magnifying glass that caused slow leaks, it wasn't sticking out on the outside, but after running my fingers along the inside of the tire several times I eventually felt something, found it and pulled it with tweezers.