I should get it by now, at least to the extent that I've developed expertise in fixing flats. (I can do it in under 5 minutes front or rear) I never know the cause of my flats, never observe a thing beyond them being flat and the necessity of fixing them - always using a new tube.
Usually my flats are found the next morning or later in the evening - so clearly a leakage rather than an impact/blow out. But from where, I never seem to locate the compromised spot, despite putting them re-inflated under water or using my ear up close.
Then the other day I was starting out, fully inflated, as I pump them to max pressure everyday, a couple blocks away, I hear Psssst and my rear is flat. I didn't hit a bump or ride over a pot hole or anything at all. (the valve was closed) Don't have a clue what happened here.
Later I got another one in front - but after a lot of riding, but still don't know the cause.
I always check the inside of the tire as well as the rim for protrusions. I use good, thick rim tape.
I'm not necessarily complaining that I get flats, or get them too often (Of course I'd rather not!) but I'd like to get better at identifying a cause.
There is a seasonal pattern I've identified, I get more flats in the warmer weather but do not do much more riding than in the winter (I'm a stalwart year round cyclist!)