Fix a flat only works if the puncture is in the tread. The construction of radial tires have bands moving in a circular direction around the tire, with a band of steel weaving around the tread. It works real well almost all of the time. However, if you get a puncture at the edge or outside of the edge, you cannot fix a radial tire. The hole will continue to rip.
The old poly tires have a basket type weave throughout the tire, so the puncture can only move to the nearest weave band. That is why all ATV tires are still poly.
Having said that, I had significant construction near my house and I got a flat about every 4 months (Nails, screws, etc.).
I now ensure I have a spare for all of my vehicles. I went so far as to buy a doughnut spare for my son-in-law's car. He laughed, but put in his car. About a year later, he needed it.
My city built a new city hall and passed the old building to the police department for 100% use. The remodeling has been underway for 18 months. My wife has had screws in her tires 3 times thus far.
While I was still riding my Harley Fat Bob daily in San Diego, I got a screw in the rear tire. The bike handling got strange and rolling it with the engine off was noticeably more work. The Dunlop rear tire was surprisingly stiff and functional even without air. I had El Cajon Harley replace the tire and they discovered the rear caliper bracket had been cross threaded by service work done before I purchased the bike. Almost $600 out the door for the tire and bracket replacement. I happily paid for another Dunlop of the same version.