Yosef asks to “be remembered” to the Pharaoh so that he can be pardoned and released from prison. Then there is a verse that says “the butler didn’t remember Yosef, and he forgot him”
To begin with, why and how could the butler forget Yosef after all his help and good that was done for him? Also, why does the Torah write that, the butler didn’t remember Yosef, and he forgot him? Of course if he forgot Yosef, he didn’t remember him!
Good questions!
To begin with, the Midrash explains a little of the background that is not obvious from a simple reading of the verses. Yosef’s being sent to prison and being kept there for two years was a punishment for not having the requisite level of “trust” in G-d that an individual of his caliber should have had.
The verse reads:
“If only you would think of me with yourself when he benefits you, and you will do me a kindness, if you please, and mention me to Pharaoh, then you would get me out of this building.” [Genesis 40:14]
Yosef was punished for two words that he said “zechartani” and “hizkartani”. The first means to remember him, and the second, to mention his name to Pharaoh. It is because of this, the Midrash relates, that Yosef was kept in the prison for two extra years. He should not have asked to be saved; he should have relied solely upon G-d’s salvation, without resorting to human intervention.
Now, to your question “how could the Cupbearer forget the good that Yosef did for him?” The answer is that it was Divinely ordained that he should forget Yosef so that the just punishment could be carried out. In fact, the Midrash relates that the Cupbearer had memory aids that he used to try and remember Yosef – he tied strings (could be the source for the concept of tying a string on one’s finger to serve as a reminder of sorts). But all these were an exercise in futility. He ultimately “forgot” Yosef for two years until it was time for Yosef to go free.
Regarding the seeming redundancy of the words, the word “zachar” can mean “remember”, but here it means “mention”. The Cupbearer did not mention Yosef to Pharaoh as he requested. Not only that, says the verse, but he did not remember him for the two years that he was in prison.