-Take the blue pill. Stay in wonderland. Pick a technology, any technology. Drive yourself into it deeper. The rabbit hole goes much, much further, than you can imagine.
-Take the red pill, and wake up: the rabbit hole goes the other way, too. On first basis, you have the ever-exploding number of scientific disciplines ( http://www.turtlshel.org/wp-content/uploads/2009/10/43056172... ). Even further, society isn't merely a collection of engineers, and scientist: other people have all kind of different jobs.
Furthermore, they are equally convinced, that their field of choice was the right one; and from their own perspective each one of them was right.
Since you're HN, you might have a particular interest towards this field we call "business". Now, this is not what people around you -who are called "managers" btw- do. A good working definition for engineers is: Business is the ability to actualize a job that needs to be done, on which you're retroactively hired (or fired) by society as a whole. Or, as PG put it: doing stuff what people wants.
Regardless of how you choose, a good partition of it is going to be soul-searching. There are 2 pieces of media I'd strongly recommend for that:
-Randy Pausch Last Lecture [ http://www.youtube.com/watch?v=ji5_MqicxSo], and
-wishcraft, which is a short book, available freely from http://wishcraft.com/.
On an ending note, I feel for you. Every time I've been down to this alley, I always always wished I'd have done it earlier. If anything, you should know this: the direction of your life does not boil down to singular moments, as you've described in your initial post. It's something that must must must be constantly evaluated, and course-corrected based on any new piece of life-data you happen to stumble across. And it's never to late to change things.