We all believe that telling the truth is fine. But sometimes there are some occasions in which you'de better keep someone in the dark about something (possibly on their own or someone else's favor) or at least do not reveal the entire matter to them!
For instance, please imagine a naive person who discloses whatever they hear or know about a specific case (with a completely good intent), ignoring the fact that revealing the whole story to that particular person they are talking to and on that special time frame is not at all logical neither for him nor for the hearer!
How an English native speaker would allude to this reality and what proverb/expression they probabely would use to convey this message to such a person:
You shouldn't always tell the truth, irrespective of the fact that telling the truth is an admirable deed.
The only sentence that comes to mind is:
All truth will not bear telling. (Perhaps a Hungarian proverb!)