Only when you solve your own problem, you create a tool or service that
you're passionate about. And passion is key. Passion means you'll truly use it
and care about it. And that's the best way to get others to feel
passionate about it too.

The point here is understanding that you're not alone. If you're having
this problem, it's likely hundreds of thousands of others are in the
same boat. There's your market. Wasn't that easy?

Example: MoneyWorks4me.com has come out of the problem Raymond
& Sreeram faced while attempting to do value investing in Indian
Stocks.

If interested read my blog with further analysis on the same: http://skprasad.boocci.com/2010/03/build-products-or-services-for-yourself/

Quote-

You need to care about it

When you write a book, you need to have more than an interesting
story. You need to have a desire to tell the story. You need to be
personally invested in some way. If you're going to live with something
for two years, three years, the rest of your life, you need to care
about it.

—Malcolm Gladwell, author (from A Few Thin Slices
of Malcolm Gladwell)

Source of this learning: http://gettingreal.37signals.com/ch02_Whats_Your_Problem.php