Several times. Not sure I have enough fingers to count. What finally got my attention was a spot on my wife's Xray. Turned out to be emphysema, at a very early stage. She quit cold turkey, I used Chantix and gum. That started on my 49th birthday. Haven't smoked since, and was off both Chantix and gum by my 50th. I'm 16 years clean.

I quit only once on Dec 24, 1973 as I walked off the ship coming back from WestPac. Never smoked again but started chewing about the time I bought a horse. Remember Walt Garrison? Quit about three years later. Waaaay harder than quitting cigarettes.