This answer mentions the idiom/saying Papier ist geduldig. The literal translation is "Paper is patient", but I gather (see DWDS.) it really means something like "Promises made are often not kept," or "Don't believe everything you hear," or perhaps "Big thunder, little rain." But what does this have to do with paper and being patient?
If I were to guess at the meaning I'd say it means that it's much easier write something down than do it, so something like "Easier said (or written) than done." Redensarten-Index is usually good at explaining this kind of thing, but in this case it only gives a connection to the Latin saying Epistola non erubescit, which seems rather different that the saying in question.
Edit: I'm reading here that similar sayings exist in other languages, though perhaps with different meanings, including Russian, Ukrainian, Polish, Dutch, Afrikaans and Spanish. I think the most enlightening quote is
"A piece of paper doesn't care what you write on it, it just lies there." (Jonathan Clark Eagle)
I interpret this to mean that you can write down anything from sublime wisdom to patent nonsense, and to the paper it doesn't matter which. But I think the German has a slightly different meaning, going by the quote
Papier ist geduldig, insbesondere in Wahljahren. Die Parteien versprechen den Wählern möglichst viel, um an ihre Stimmen zu kommen. (Die Welt, 03.02.2018, via DWDS)