When I start hearing Tour de France music in my head, and improvising Phil Ligget dialog, and feeling like I'm just crushing it that day, but I'm only 10 miles into a long day in the saddle, it can be tough to back off. I'm terrible at this myself, I often over estimate my fitness, and how long my food and water will last. Long rides are not really my specialty, most of the fun is over for me by about the 3rd or 4th hour anyway. And I've probably gotten most of the alleged health benefits of the ride by then too.
At least you had other riders around had you had some sort of medical emergency, it can be scary to have that happen to you in an exposed location miles from anyone else.