I read the title and knew the word was "no". Did I end up reading a boring, unimaginative treatise on "never say no"? No. Thanks.
Actually it's not about "never say no".
It's about "never accept no". Or rather "never say no to yourself".
It's still horrible advice. There is no such thing as universally good advice. Everything must be taken in context, and saying/accepting "no" is often the best path.
You're right. Blindly following an advice taken literally is never a good idea. However as a general mindset I think it's really valuable tip for many people who unnecessarily limit themselves.
How's about saying "no" to the clueless. I accept that.