How does Shakespeare's use of the specific simile "I am constant as the Northern Star" support the statements he makes in the rest of his speech?

"I am constant as the northern star,

Of whose true-fix'd and resting quality

There is no fellow in the firmament."

These frase used by Shakespeare show how Ceaser felt secure and didn't prepered to be more carefull toward his opposition, he felt as constant as norther star is for mariners and that no harm can be done for him that's why he ignored three warnings