It's true that people forget the kindness that we show to them and this is exactly what happened in Joseph's case. He was in prison for no fault of his, but an opportunity had risen for him to have a recommendation given to Pharaoh regarding the injustice that had taken place in his life. This is what happened...
The cupbearer and the baker of the king of Egypt offended their master, the king of Egypt. Pharaoh was angry and put them in custody in the house of the captain of the guard, in the same prison where Joseph was confined. The captain of the guard assigned them to Joseph, and he attended them. After they had been in custody for some time, each of the two men had a dream the same night, and each dream had a meaning of its own. When Joseph came to them the next morning, he saw that they were dejected. So he asked Pharaoh's officials who were in custody with him in his master's house, "Why are your faces so sad today?" "We both had dreams," they answered, "but there is no one to interpret them." Then Joseph said to them, "Do not interpretations belong to God? Tell me your dreams."
Joseph interpreted their dreams and gave a favourable interpretation to the cupbearer and then told him to speak a good word to Pharaoh regarding him. Pharaoh restored the cupbearer to his position, just as Joseph had said to him in his interpretation. The cupbearer, however, did not remember Joseph; he forgot him.
Joseph must have waited for many days thinking that the cupbearer must have put in a good word for him to Pharaoh, but that was not the case. Yet, God did not forget him and had him released from prison when Pharaoh himself had troubling dreams which no one could interpret and Joseph was called to interpret them.
God is faithful and even though people may forget what good we do for them and not help us in return when we are in need, God will be watching over us to deliver us at all times and his promise to "never leave us nor forsake us" will always come true if we trust in him continually.