Solving your problem is a good way to find ideas. You know the problem well and the context the problem is in. However, if your work life, social life or life in general is not too varied, finding a problem to solve can be a problem in itself. Not being respectful and some people live quite contented lives like these, but living a simple, straight forward, suburban life style can be hard to find pain problems.
So to increase the ways of gaining problem to solve, getting out there to experience different aspects of life and talking to other folks are two sure way of find problems to solve. The side effect is that you will be a more rounded character and will, most probably, enjoy life much more.
Basically, this is what Nathan is saying.