You can find the exact odds of performing each feat somewhere online, I just don're remember where. I know that they put the odds of a hole-in-one as being much more difficult than bowling 300. The main reason is because their are so many variables (distance, wind, hardness or softness of greens, etc) involved in a hole-in-one. I still think it's a bit overblown, however, as I know some terrible golfers who have found a way to snake in an ace. Then again, I also know some crappy bowlers who have brooklyned, and nosed their way to 300, so go figure. For me, I still think that bowling 300, for most people, is much more difficult because you have to find a way to get the job done 12 times in a row. Plus, who steps up to the tee thinking "alright, I'm going to knock this sucker in the cup"? Bowlers, on the other hand, certainly know what's at stake as their string of strikes grows. Like I said, knocking in a hole-in-one is a remarkable accomplishment, but, for me, finding a way to succeed 12 times in a row is harder, even on easy conditions, than it is to find a way to get one shot to go in. Hopefully, I'll shoot about a dozen 300s in the next few years and then I'll change my tune.
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I can't bowl 300, but I can bench 310 : )