A prisoner's greatest hope is pinned on a man who has just been restored to power, yet the anticipated moment of rescue turns into profound disappointment. The chief cupbearer completely ignores the very person who deciphered his dream and offered him a lifeline. This failure to act weaves together complex human psychology with exacting Divine providence.
The narrative emphasizes a twofold failure on the cupbearer's part. Chronologically, he failed to advocate for Joseph immediately upon leaving the prison, and as time dragged on, he forgot him entirely [רש״י, רשב״ם, הדר זקנים]. He lost the memory of Joseph at the exact time and place where it was most crucial to recall him [שד״ל]. The primary approach among commentators distinguishes between an external action and an internal state. First, the cupbearer did not speak of Joseph to Pharaoh, and second, Joseph was eventually erased from his heart and mind completely.
Commentators differ on the human mechanics behind this memory lapse. Some judge the cupbearer favorably, viewing it as a natural, unintentional mistake [ריב״א, בכור שור, הטור הארוך]. His mind may have been so overwhelmed by his reinstated status and his present duties that no room remained for memories of the past [רש״ר הירש]. Furthermore, simply because he never crossed paths with Joseph again, the memory naturally faded [ביאור שטיינזלץ]. Since retaining a memory requires active effort or making a physical reminder, which the cupbearer failed to do, he simply forgot [הכתב והקבלה]. Conversely, others view his behavior as an act of absolute ingratitude [קיצור בעל הטורים, צאינה וראינה]. According to this perspective, he deliberately chose not to mention Joseph, perhaps harboring a disdain for the Hebrews. This conscious decision to suppress the matter is what ultimately caused him to forget Joseph entirely [אור החיים, כלי יקר, ביאור יש״ר].
Beyond human nature, commentators agree that this forgetfulness was the result of direct Divine intervention. Even though Joseph was exceptionally righteous, he was punished for placing his trust in flesh and blood rather than relying exclusively on God [רש״י, צאינה וראינה, העמק דבר]. God is profoundly exacting with His most pious followers. Because Joseph treated the cupbearer as the ultimate source of his salvation, Heaven intervened to dismantle the plan [משכיל לדוד]. A Midrashic tradition vividly illustrates this intervention, describing how the cupbearer actually tried tying knots in his clothing as a reminder, but an angel came and untied them. This ensured that the man would forget, allowing God to be the sole author of Joseph's eventual rescue, proving that true salvation comes only from Him [מלבי״ם, מחוקקי יהודה, נתינה לגר].
As a direct consequence of his misplaced trust, Joseph was decreed to remain in prison for two additional years. This specific duration corresponds perfectly to the two separate times Joseph pleaded with the cupbearer for help using the language of memory [כלי יקר, שפתי חכמים]. Another explanation suggests that Joseph naturally expected the cupbearer to act within the first year, as it is a known human trait that a person is forgotten from the heart after twelve months. Thus, his first year in prison was spent waiting on a human promise, and the second year was added as a specific penalty for that misplaced hope [גור אריה]. Ultimately, the cupbearer's human forgetfulness was necessary to make room for Divine remembrance, a shift that would later draw Joseph directly from the dungeon to the royal throne [אור החיים].