What aspects of Shakespeare's character does Sonnet 18 reveal?

In Sonnet 18, Shakespeare states that his verse is more powerful than death. He begins by asking whether he should compare his friend to a summer's day and then decides he should not, as summer does not last forever and is not perfect. Occasionally, there are winds in summer, and sometimes the clouds obscure the sun. Unlike the summers that people experience, "thy eternal summer shall not fade," meaning that the friend's prime will never go away because Shakespeare will immortalize his friend's perfection in verse. He says that by immortalizing his friend in verse, the friend will never die. As long as people still populate the earth, "So long lives this and this gives life to thee." In other words, Shakespeare's sonnet will endure, as long as people can read it. Shakespeare believes in the power of his own words and believes the poet is more powerful than even death. His message suggests that Shakespeare was confident about his ability to produce verse that would stand the test of time.