What are three problems that the poet finds with a summer's day in Sonnet 18 in lines 1-4:
Shall I compare thee to a summer's day?
Thou art more lovely and more temperature:
Rough winds do shake the darling buds of May,
And summer's lease hath all too short a date:
First, the speaker says of his beloved that she is more lovely and more "temperate" than a summer's day. Temperate can mean the use of restraint. The speaker then goes on to say that the sun can be too hot or too hazy in its blazing heat:
Sometime too hot the eye of heaven shines,
And often is his gold complexion dimm'd; (5-6)
Therefore, a summer's day might be too hot or too hazy and humid; whereas, the speaker's beloved is more temperate, restrained, not tending to go to either of those extremes. The other complaint the speaker has is that summer does not last long: it "hath all too short a date." The speaker adds that the "summer" of his beloved (the beauty of her life and/or the memory of it) is eternal. So, summer is fleeting relative to the eternity by which his beloved will be remembered: even if it is in the "lines" of the sonnet ("this") itself:
Nor shall Death brag thou wander'st in his shade,
When in eternal lines to time thou growest:
So long as men can breathe or eyes can see,
So long lives this and this gives life to thee.