This is a good question and a few points could be made to show his character flaws. I will mention three of them.
First, Caesar should have know that anything that hinted of kingship was distasteful to the Roman people. He should have also known that being dictator for life was going of to breed envy and potentially something worse.
Second, Caesar should have paid more attention to the omens, prodigies, warnings of seers, and even his wife's dreams. All of these presaged that the gods were not pleased and that his end was nearing. It is remarkable that he did not heed these warnings, when there were all over the place. In addition from a historical point of view, any good Roman would have known this, especially Caesar, who was the chief priest of Rome (pontifex maximus). This is inexcusable.
Finally, he should have known that something was wrong, when even Brutus was marked among the conspirators. Of course, Caesar was surprised at this, but that is exactly the point. He should have known that he went too far.