Most startups begin with the founder(s) thinking about some product or service they feel people will need. When they fail to gain traction many months, sometimes years later, it is almost always because often because they never did any real marketing research or spoke to target customers about whether their offering was relevant. Most probably, they had no idea of who the target customer was anyway. When it dawns on the founder(s) that the market does not really care about their product, it is usually too late and the startup fails.

 
Startups should almost always be a way to put together an initial organization to find a business model that is sustainable. This does not just occur. You have to go out and meet potential customers, iterate over who your ideal target client is, what are their problems and needs, what value you can offer.