I can go months and months without a flat, and then have three in one week. I haven't kept track but I may have had as many as 15 flats this year. And they usually come in bunches.
The most common cause is picking up glass or some other sharp object (like a staple) that punctures through the tire into the tube. While a bike lane on a busy road is a godsend, one downside is that debris migrates to the edge of the road into the bike lane, and bikes don't have enough mass to sweep the debris further off the road. I hate it when I find myself riding through small specs of shattered glass, either from a car accident or carelessly tossed liquor bottle.
I had another rash of flats due to defective tubes near the valve stem. That was sure discouraging, with multiple flats in one week. Another time I had a couple of flats due to the rim strip not covering the spoke hole edge completely.
On one group ride I had two flats on the road and had to borrow another spare tube. Turns out I didn't find the source of the first flat so it punctured again (small piece of glass). In a pinch I could try to patch a tube on the road, but that is a pain. I carry a spare tube, tire irons, and a pump to get back on my way. Then I try to patch the tube when I get home to salvage the tube for further use.
Here is a nicely repaired tube.
May the fates keep yours and my bike tires fully inflated day after day!