In the first act Lear is blinded by his pride. He wants things to go one way - to be one way - and when his vision is not carried out to perfection, Lear gets angry. The entirety of Lear's tragedy is predicted by his own flaws, which are clearly articulated in the first act.
Too proud, too bold, too full of self-regard, Lear fails to see the virtue in Cordelia and fails to see his own folly.
That King Lear appears as a flawed character in Act I should surprise no one. There are no perfect characters in this play, or indeed, in any of Shakespeare's plays. They are all flawed, as all humanity is flawed in the larger world. However, the king's flaws are more important than the average person's, because his mistakes reshape entire kingdoms. When Lear says "Only we shall retain / The name, and all the additions to a king" he is demonstrating a dangerous and fundamental misunderstanding of kingship and power. You can't give it away and keep it at the same time, but that's what he tries to do. The result is a kingdom in chaos, and, eventually, many deaths.
Firstly one must keep it in mind that 'King Lear' is a tragedy which aims to fill in the reader's mind with fear and sympathy. When we look at King Lear we definately presume that a king is always perfect and that if he will do some mistake then it would be major,technicle,political or any other but not such a silly one or such a blunder. But Shakespeare, being a great master of human being's psychology, shows us how such a great King suffers from a simple and pardonable moral flaw of flattery which ultimately becomes the cause of his death. The king's madness at the end and also Cordelia's death, lear's grief over it and his ultimate death create fear in the reader's mind and also furnishes a lesson to us.