In 27:33-41 we read about Yaakov fooling Yitzhak to get the blessings. Esau finds out and totally freaks out. He gets upset and threatens to get even with Yaakov. He pleads with his father Yitzhak to find another bracha to bless him with.
We tend to have a picture of Esau as an evil person who was a bit bloodthirsty. Maybe a megalomaniac. Idol worshipper.
Yet Esau ran off to serve his father and fulfill his wishes. Commentaries say that despite Esau's overall bad disposition, the one mitzva he excelled at was honoring his father. He went all out in that regard. That was why Yitzhak thought that Esau deserved the brachos. Even if he did not realize how evil he was, he must have at least thought he is an ok kid and deserving of the brachos, because of the great mitzva of honoring parents that he adhered to very carefully.
But there is more to it than just that. Esau really believed in the brachos. He was not simply scoffing at them when he sold them for the bowl of lentils saying they are worthless. Look at how upset he was when he understood they had been given to someone else. he must have believed they would happen or else he would not have gotten so upset. He pleaded with his father to come up with a new bracha for him. he threatened Yaakov. etc.
It seems to me that brachos are not just someones good wishes for you. It is not that someone, maybe a great person, is just wishing you well and maybe Hashem will isten because he is great and has influence. No. I think brachos are generally indicative of a certain reality that may not yet have come to fruition and the bracha expresses the impetus for the recipient to strive in that certain direction to attain that reality.
Esau realized he lost the brachos. he lost the potential for all that wealth and fortune. that is why he could not understand why Yitzhak could not just give him another bracha. He asks "Is there nothing else for me?" (27:38). He was desperate for that potential and thought there had to be something available for him. But Yitzhak says no I cannot. That bracha is his and proceeds to bless him with another smaller blessing. A bracha is not just a wish of goodwill that Yitzhak could bestow uon whomever he wanted. It is a reality of what Hashem has to offer. Once he gave it to Yaakov, he could not just share it with Esau.