1. Materials Science - "Mat Sci" tends to drive a lot of technology. Until materials can be invented to do things that we want technology to do, a lot of great ideas stay in the lab. Whether it is teflon or the heat tiles on the Space Shuttle, it is the availability of materials that make technology work. Aluminum - once one of the rarest metals on the Earth, became one of its cheapest. And everything from airplanes to beer cans became possible not because the technology wasn't there before, but because the material to make the technology didn't exist.2. Miniaturization - almost everything you can do with a computer today could be done with a computer back in the 1960's or 1970's. The difference is, of course, the computer back then would fill an entire building, cost millions of dollars, and take overnight to render just the welcome screen on Windows. Microprocessors with more power than a "supercomputer" of the 1970's are now no larger than your thumbnail, if that, and even a mundane run-of-the-mill car may have dozens of them. Once the technology is sufficiently compact, it can be integrated into products.3. Cost and Volume - once you make enough of something, the cost goes down considerably. When you are offering traction control as an option on select Buicks in 1973, well, you sell maybe a few hundred a year. When it is standard equipment on all models, well, the parts cost drops off significantly. There is a tipping point where volume of production and costs reach a point where the product becomes affordable.
4. Consumer Acceptance - this is arguably the hardest part for some technologies. Consumers don't like to feel they are being forced to do something. At the same time, they will latch onto the "latest and greatest" technology in an effort to appear to be sophisticated and modern. But if you can't get people to like the technology, it may fail from the get-go. Self-driving cars, for example, is an exciting technology. Yet there is a drumbeat of discontent among some people against these cars (and indeed, hybrid and electric cars as well). Overcoming this will be the key to implementing the technology - the "tech" issues are really secondary.
This last item is the real stumbling block. When I was very young, my parents took me to the 1964 World's Fair in Flushing Meadows, New York. One of the exhibits was the world's first picturephone, which allowed you to call someone and see them as you talked to them. The technology was crude and expensive, but over time, the costs came down. Funny thing, though, people didn't clamor for the service.
Today, you can picturephone anyone with an app on your smartphone. You can Skype on your laptop or PC. For some reason, these apps are not as popular as people thought they would be. In fact, texting has surpassed even voice calls as the main source of communication these days. It seems that we don't want more communication but less and less personal communication.
As it turns out, and as the folks at the "Bell System" discovered by the 1970's, people simply didn't want to look at each other on the phone. Chalk it up to answering machine stage fright or whatever, but for some reason, it was not the "must have" application that everyone thought it would be, even as the Jetsons demonstrated it.
(I suspect that video calls are popular, but not for the reasons that the inventors originally thought they would be. Porn and sex seems to drive a lot of the Internet and today Smart Phone apps. Sexting and video sex seem to be the major applications for many of these new phone features. Why do you think middle-school kids favor an "app" that erases their photos automatically? Because they don't want Mom and Dad to see what they've been up to!).
Whether Virtual Reality takes off where the "picture phone" failed remains to be seen. However, I think that once again, sex will rear its ugly head, and if VR is a hit, it will be porn-driven, sadly.
As for other technologies like self-driving cars and whatnot, again, it will depend on consumer acceptance more than anything. We all say we want a self-driving car, whether we are willing to spend twice as much to have one is another question.