The easiest way is to have outside advisors who can and are willingto adversarially challenge the assumptions you're making. If you don't have those, good cofounders can sometimes play the same role (although that is harder since they are likely to share similar biases as you).
https://en.wikipedia.org/wiki/List_of_cognitive_biases
Most people start a small business for tax reasons, and the few lucky loud clowns claiming hyper-scaling BS is sustainable simply disappear within 5 years.
Best advice, answer the simple question "will random people buy this when no one is looking?"... if you have to explain/sell a product/service more than 5 seconds, than that business model likely isn't sustainable.
I also see a lot of smart folks that think they will get paid for excuses... only lawyers, PR, and politicians are in that business. =3
For B2c, maybe. B2B is very different - they aren't going to make up their mind in 5 seconds and you aren't going to have a product that can be explained in 5s.
If not, than one is explaining/selling again, and you will only ever have 2.7%*(time/sales_pitch_time) customers. Letting client/customers dictate the terms of a product/service often will just turn your business into a staffing agency.
B2B is actually more risk, as any deal exceeding 12% of revenue sets a timer on how long your business will likely survive. Some unlucky folks also end up acting as a product warehouse for clients, contract labor, or a scapegoat for client internal strategic mistakes.
If people can't summarize what they do in 1 sentence, than they likely have a fuzzy definition for a business project goal. For example, people that use more than 4 conditional statements (if/but/when etc.) to describe something, than I have observed they often last less than 3 years regardless of cash burn rates. =3
I broadly agree with your point, but disagree with this sentence. IME a 1-sentence business goal is almost certainly too fuzzy to be useful. There's nothing actionable about "We help you survive audits and readiness for regulation $FOO", which is frequently the business goal.