Answers are easy. Finding problems are hard.
- Isn't there a problem with the headline? Maybe they're not that hard to find after all. If not then there is one with my english, which would still mean that finding a problem is not too hard :-). - Anyways I am not sure if it is really easier to solve a problem than to find one. I would say the hardest part would be defining a problem in way that it is approachable. You can come up with a lot of very general problems, the hard part is narrowing it down. 
- Finding good problems for the answers you already have (built) is hard, also known as seeking market fitness :) - I stumble on good problems with no obvious answers frequently, and my take is that approaching them with the mindset of "hey, what if...?" is what is really uncommon. Not hard, children do it all the time. - What's hard? Keeping that mindset of "what if...?" alive over the years! :) 
- You don't have to solve a problem to have a product. E.g. http://sethgodin.typepad.com/seths_blog/2007/08/just-in 
- Grammar are hard. 
- undefined 
- Most problems are trivial or impossible. Progress happens on the small margin of problems that are in between. 
- Richard Bellman, I think, is famous for pointing this out frequently. 
- The phrase "it turns out" has gone viral. Unfortunately somebody else got the domain before me.