One issue is the lack of domain expertise. To really understand a problem you need to be a domain expert. Young people, who are a large part of the tech world, don't really have a lot of that.

You can also learn what problems are worth solving by talking to people (ie: customers). How many customers have you talked to today?

That's why so many startup books talk about customer focus, customer acquisition, erc. Someone needs to buy it. Who is that someone?