Many, many books have been written on the topic of building a startup. People world-wide, from vast and varied backgrounds, have all had ideas for new and exciting products, many digital, some brick and mortar.
As my professional expertise is in the development of web and mobile applications, I hear ideas from basically anyone on a regular basis. It usually starts with, "Wouldn't it be cool if x did y?". And of course, I say, "Yes!", because in reality, it really WOULD be cool if x did y. So why don't you go out and create x? Why doesn't anyone actually DO what's required in order to build and ship a product?
The answer is: you.
You are the problem. You are also the solution. Allow me to explain.
When you get an idea for a fantastic digital product, you're filled with glee. You see the world as sunny-side-up, you're instantly excited about building this thing and getting rich and changing your life. Granted, those things do happen to some people, albeit a very, very seldom few.
But also significantly fewer are the number of people who actually launch the product that's burning a whole in their mind. Why? Because they are afraid. Yes, it's a lot of work launching a startup. But more often than not the creator of said startup talks themselves out of it. They get scared. Are people going to hate my idea? Are they going to laugh at me? Am I going to waste all of my time and in the end, no one will use it? It's highly likely. But you'll never know unless you try.
As simple as it may sound, once you have the product idea set, the design set, and you're ready to develop and push forward, the solution is: DO NOT LISTEN TO YOURSELF. Turn your brain off and just execute. Do not stop the train once it has left the station.
At some point during the early stages, sit and write two boxes on a piece of paper. YES and NO. Sit there for 10 minutes and really think about whether you want to launch your startup. Check the YES box if you really, really want to do it. Check the NO box if you're not certain.
But if you check the YES box. You're committed until you launch it. The only other alternative is death.