Caesar hated to look weak. He could have taken precautions or not even went that day but the images of Caesar throughout the play are those of constancy and greatness. Caesar himself exclaims, "But I am constant as the northern star" (3.1.60), "Hence! wilt thou lift up Olympus?" (3.1.73). Cassius even angrily compares Caesar to the Colossus, saying, "Why, man, he doth bestride the narrow world / Like a Colossus, and we petty men / Walk under his huge legs and peep about" (1.2.136-138). Thus when Caesar falls, the world falls into chaos. There is no one able to replace Caesar's power immediately after his death, and so anarchy reigns until Octavius eventually seizes power in the final lines of the play.
Caesar's greatest flaw is his refusal to acknowledge his mortality. Often referring to himself in the third person, he develops a sense of greatness and godliness that distracts him from taking appropriate precautions.