Name that literary quote!

Cafe Society
1

Hi folks, I’m trying to track down the source of an oft-repeated quote, and the exact wording:

“Believing so, doth not make it so.” or something like that. Perhaps, “Speaking so…” I can’t remember. Old timey English of course, maybe Shakespearean. It’s been bugging me. Anybody recognize it?

Thanks in advance.

2

Moved MPSIMS --> Cafe Society.

3

Don’t know if this is what you mean, but Hamlet said “there is nothing either good or bad, but thinking makes it so”.