I fly mostly short-haul domestic US flights to the tune of 90k miles/year. If I consider an IRROP to be, say, a 30+ minute delay that also impacts on-time arrival, I'd say I experience one every 15-20 segments. Double that if you count *any* delay whatsoever - but I tend not to count those because often a 10-15 min delay is made back up in the air and we still arrive on time.

Of course, there are instances where they stack - late summer trip with a late afternoon connection and a storm system passing through? It's not a question of if IRROPs will happen, it's to what extent and will your 2nd flight be delayed enough so you can still make it from your delayed 1st flight.

Thankfully, I've only experienced one cancellation in the past year or so, and I simply rebooked to a different routing and arrived an hour later than planned.