Startup Playbook by Sam Altman

One of the first things we ask YC companies is what they’re building and why. We look for clear, concise answers here. This is both to evaluate you as a founder and the idea itself... Another thing we ask is who desperately needs the product.

Although I don't agree much with Sam Altman from what I read about him, I like this quote from the article. There's so many people in this world who suffer in their daily lives, and there's lots of ideas that can help them. Asinine app startups like Yo, which get millions of dollars of funding, are taking money and attention away from entrepreneurs that could be doing impactful social good with those resources, which is upsetting to think about.
In practical business terms, too, building a product or service for an audience of 0 is not a recipe for success. Even if a business is built correctly, if it is not advertised to the target audience in the right way, they won't think it's for them and won't make use of it.

The same idea reiterated a bit:

What if you don’t have an idea but want to start a startup? Maybe you shouldn’t.

This one is just... really painful to think about. Like a chicken running around with its head cut off. According to the post, YC tried funding companies like this, and unsurprisingly, they failed. I'm sure it can be hard enough to stay passionate and involved with a groundbreaking idea all the way through the startup growth process, but it would be much, much harder to stay motivated with no idea at all.