Highlight the part you want to summarize. Like the part with out the Notes.
Also Paul's writing is pretty poor. The ideas are good, but he jumps around and uses short sentences with far too many pronouns.
Garbage in Garbage out.
Here is the 25% version, which I think is Readable:
The way to get startup ideas is not to try to think of startup ideas. And yet by far the most common mistake startups make is to solve problems no one has.
I made it myself. But galleries didn't want to be online. Because I didn't pay attention to users. Because they begin by trying to think of startup ideas. That m.o. is doubly dangerous: it doesn't merely yield few good ideas; it yields bad ideas that sound plausible enough to fool you into working on them.
At YC we call these "made-up" or "sitcom" startup ideas. But coming up with good startup ideas is hard.
For example, a social network for pet owners. Millions of people have pets. Choose the latter. Not all ideas of that type are good startup ideas, but nearly all good startup ideas are of that type.
Made-up startup ideas are usually of the first type.
Nearly all good startup ideas are of the second type. If you can't answer that, the idea is probably bad. But you almost always do get it.
But while demand shaped like a well is almost a necessary condition for a good startup idea, it's not a sufficient one. If Mark Zuckerberg had built something that could only ever have appealed to Harvard students, it would not have been a good startup idea. Facebook was a good idea because it started with a small market there was a fast path out of. So you spread rapidly through all the colleges. Often you can't.