OP, I used to feel just like you. However.....
Through lots of practice, posting in the forums, joining an active country club, and an increased understanding/knowledge of the game and it's courses, I can tell you it's very much possible for any player to achieve.
I played a round at Oakmont yesterday and carded a 30. I ran a bit hot but it still felt like any other round as it was happening. I missed one birdie putt because I forgot to note the green speed, and I made one bogey due to a stupid risk. Take away two simple mistakes and it's a 28.
I know it wasn't a 28, but the fact is I never got all nervous or even really noticed how well I was doing. All a sub-30 nine requires is some solid shots (not even a lot of dinging), hitting it close to the flag, making the putts you should make, and a bit of good variance for a lucky shot here or there. Two lucky shots and/or a good par save and you are seriously there.....on any given day.
It could happen to me tomorrow. It probably wont, but I can see that it could strike me at any time.