In theory I would agree, but most of the time I need to have a special account with the vendor to see the docs, and the docs are never up to date, even when they're dynamically generated somehow. Plus I'm not always using an API that expects me to be using it. Sometimes the API goes out of it's way to prevent me from using it, but the vendor gives me their blessing to try.

Interacting with systems like this for a decade has conditioned me to just try it out first, and then look up what i need to know if i'm having trouble, or need to optimize.