The core idea all effective ideation methods have in common is that they focus on finding problems over ideas. This is one of the few things almost anyone (Pieter Levels, Rob Walling, Courtland Allen, Seth Godin, Nathan Barry, Paul Graham, Patrick McKenzie, to name a few prominent figures) can agree on.

"Customers don’t pay for ideas; they pay for their problems to be solved." - Nathan Barry

Far too many aspiring entrepreneurs still do it backwards and start with an idea, a solution looking for a problem. After months of working on their product, they start to wonder: "How do I find customers for this thing I built?"

Oftentimes this is incredibly difficult because they solved a problem no one has. Using a lots of clever marketing tricks they might be able to convince a few people to buy their product. But generally it will be an uphill battle and something that can and should be avoided.

It's far more effective to de-risk product creation by starting with a painful problem (ideally one that is well-understood but currently poorly solved).

Focusing on problems also makes sense because the most dangerous kind of product idea is what the folks at YC call "sitcom startup ideas". These are the kind of ideas that sitcom writers come up with for one of the characters that sound somewhat plausible but are actually bad. Sitcom startup ideas are "cool" ideas that in the real world no one is willing to pay for. (The Japanese call this kind of idea chindogu" (珍道具).)

[T]he way to get startup ideas is not to try to think of startup ideas. [I]f you make a conscious effort to think of startup ideas, the ideas you come up with will not merely be bad, but bad and plausible-sounding, meaning you'll waste a lot of time on them before realizing they're bad." - Paul Graham

For an analogy, consider how much easier it is to sell painkillers compared to vitamins.

It's easy to become seduced by an idea that seems clever on the surface. However, if you focus on painful problems that people in the real-world are having, the chances are much higher that you'll eventually be able to sell your product. The word "painful" is essential here because certainly not every problem represents a business opportunity.

"Startups are as impersonal as physics. You have to make something people want, and you prosper only to the extent you do." - Paul Graham