We read in Parashat Vayigash of Yaakov's arrival in Egypt and his meeting with Pharaoh, at the conclusion of which Yaakov gives Pharaoh a blessing (47:10). While the Torah does not specify what kind of blessing this was, Rashi, based on the Midrash, explains that Yaakov blessed Pharaoh that the Nile River should rise and overflow its banks in his presence. Indeed, Rashi adds, from that point on, whenever Pharaoh would go to the Nile the waters would rise in his honor. This comment of Rashi should likely be read in conjunction with his comments later in this parasha (47:19), where he writes that the famine in Egypt came to an end with Yaakov's arrival.
Rav Yosef Shaul Nathanson, in his Divrei Shaul (mahadura tanina), speculates that this phenomenon continued during the time of the subsequent Pharaoh, as well, who subjugated Benei Yisrael. As Rashi comments (based on the Midrash) in Parashat Vaera (Shemot 7:15), Pharaoh declared himself a deity of sorts, and for this reason had to perform his bodily functions in private. Quite possibly, Rav Nathanson suggests, Pharaoh made this claim on the basis of the river's response to his presence. Whether or not the king believed his own claim of godly power, he was able to "prove" this claim by approaching the river and showing that its waters rose in his honor.
If so, then Pharaoh's behavior exemplifies the tendency that people often have to credit themselves for the achievements of others. People often feel so inadequate and inferior that they are prepared to try bolstering their self-esteem by taking pride in achievements for which they deserve no credit. Just as Pharaoh declared himself divine on the basis of a blessing he received from Yaakov, so do many people attribute certain qualities to themselves for accomplishments in which they themselves played no significant role. The lesson of Pharaoh is the need to draw a clear distinction between one's achievements and one's blessings, to feel pride for what he has accomplished, and feel grateful for that with which he has been blessed.