No business idea that can be pitched in one sentence can be brilliant. Any idea that can be shortened down that much is not brilliant, which is why so many pitches are of the kind "We are an ex-Google/Facebook/Amazon team building the Uber/Airbnb/Facebook for niche x". Yawn.

Truely brilliant ideas are very, very rare and take quite a long time to explain.

Edit. My approach is to say that I have solved problem x. If the person is interested in this then I then ask if they want to learn more and tell them approximately how long it will take to explain. Most people aren't interested, but for those that are it is always a productive and enjoyable experiences to talk to them about the idea in depth.

In business school (I know, shudder, I went to biz school), there's a pretty textbook formula of "[Product/Service] does [what's unique about the product/service] to [competitive advantage/how it's solving the problem]." It's simple, but it's actually much harder to do than you'd think. When you nail it, it's incredibly compelling.

After you build a draft, you have to ask, "Is anyone out there already saying this? Do they have our [what's unique] or [how it's problem solving]? If so, you need to either keep workshopping and thinking about what's truly unique to your product, and if the problem you're trying to solve is 1) actually a problem or 2) a thought-out solution.

If you're really struggling to answer those questions or come up with a unique statement, it's a good indicator that your product/concept may not be viable.

I'd say keep it to one sentence. I heard some one say that if you can't tell me what your business does in one sentence, you haven't found the niche.

https://techcrunch.com/2012/04/24/one-sentence-pitch-winners...

Google: one sentence business pitch

Funnily enough none of those pitches resonate with me. They all seem a bit long

Just found this video, it's pretty good advice https://clip.mn/tag/MDhkMDQ2ZTI

Density of information. It needs to not only be short, but to convey a lot at the same time. This is why analogies (like "Uber for x") are popular. You need to capture something of the spirit of the venture, as well as what differentiates it from its competitors.