Also, mashing up two abstractions is a good way to narrow down the solution space you are interested in.
For example, IT combines information with technology. PT combines people with technology. CP combines communication with people. TT combines two technologies.
Each mashup has a different set of value propositions that work well with it. IT generally uses tech to manipulate information to answer a question or help people make sense of something. PT generally revolves around augmenting human ability. etc.
I've found it surprising how much this can be honed like any other skill. At first thinking up ideas seems difficult, then suddenly you've got a queue of things you want to build because you're annoyed. Then you go through the queue for things that other people are likely to be dissatisfied with as well.
Hopefully once you're at that point you're better equipped to spot broken stuff that you don't necessarily use (or even want to use). My guess is that not being put up their own online store was not a pain point for Paul and Robert but years of building whatever tools like lacked helped them spot it as a problem others were having.
There are many ways ...
- make things for yourself & solve your own problems
- take notes in notebook
- observe from nature
- don't be obstinate (in-flexible)
- revise your ideas & filter
- listen to your users
The thing is some ideas are crap. Others maybe ok. But it's what you do with the idea that matters. Turn the idea to a demo. Release the demo and see how many users pick it up. Re-visit your old ideas
It's how quickly you can turn idea to demo. Unleash your ideas in the form of a demo on your users. You'll find out quickly if they are crap or not.
I would say about ninety nine percent of my ideas are really bad or crazy sounding. When I look back at my notebooks, most of my ideas are juvenile, ill-concieved, and smack of mental illness. But there are always a few golden ideas glinting amongst them.
I warn people against concentrating on good ideas because that prevents them from practicing the raw creation of ideas. Good ideas will be revealed as your collection of raw ideas interacts with the world.
The Map of Innovation: Creating Something Out of Nothing. http://www.amazon.com/Map-Innovation-Creating-Something-Nothing/dp/1400048311
(It's a joke. Laugh.)
http://www.iamworththewait.org/101.html
It does a pretty good job at spanning the range of human activity.
Good luck!