After the brothers got rid of Yosef, the Torah tells us that Yaakov refused to be consoled. The Passuk specifically says "And his father cried for him". That, seemingly, means Yaakov continued to cry for the loss of Yosef.
However, Rashi points out that this does not refer to yaakov's crying, rather to Yitchak (Yaakov's father) crying. Rashi says that Yitzchak cried because of the pain of Yaakov. Yitzchak knew that Yosef was alive (it is unclear whether he knew all that had transpired or just knew with ruach hakodesh that Yosef was alive) but he could not tell Yaakov and therefore cried for Yaakov's pain.
We find in the Torah a number of occassions where a person knew what was going on when nobody else did, but mysteriously kept quiet. Yosef spent 22 years in Egypt but never contacted his father to tell him he was alive (and we saw from the reunion of Yosef with his brothers that Yaakov was at the forefront of Yosef's thoughts the whole time). Yaakov knew the secrets of the end of days, but kept it to himself on his deathbed. Yitzchak here knew about the sale of Yosef, but kept quiet. There are probably more examples, but that is all I can think of right now.
It seems that just because you know something, does not obligate you to tell everyone about it. There are times where silence is golden, even if you think there is great benefit to telling.. Yaakov, Yosef, Yitzchak, etc. knew things that could have saved others pain and suffering but did not because God wanted a certain gameplan to play out. it was more important for them to let things play out then it was to ease some personal suffering.
There are times where it is better to keep quiet.