I agree with the sentiment, but a there is a caveat: not all documentation is created equal.
There's incomplete documentation. There's API documentation without examples (ie specification but no example/tutorial). There's outdated documentation!
I can also say that I started studying SQL by reading the docs for mysql, and after an hour I was still stuck inside INSERT or SELECT. Reading about all use cases in detail was not useful to learn a first approach to the queries!
So I'd say that this "truism" isn't always true. Sometimes the docs suck or don't provide the info you need at that time.
There's incomplete documentation. There's API documentation without examples (ie specification but no example/tutorial). There's outdated documentation!
I can also say that I started studying SQL by reading the docs for mysql, and after an hour I was still stuck inside INSERT or SELECT. Reading about all use cases in detail was not useful to learn a first approach to the queries!
So I'd say that this "truism" isn't always true. Sometimes the docs suck or don't provide the info you need at that time.