Answer:
The paradox in the last two lines, the couplet of the sonnet means that the lover is unable to see his lover during the day, for he has to stay awake and see unnecessary things. But when it's nighttime, he can clearly see her as bright as day for then, he will see her in his dreams when he closes his eyes.
The speaker feels helpless and devastated at not being able to see his beloved and longs for the nighttime when he can see her in his dreams again.
Explanation:
A paradox is when two contrasting things are juxtaposed, presenting the contrasting ideas within close quarters which can at times be even absurd. In this sonnet by William Shakespeare, the whole sonnet is full of paradoxes.
The paradox in Sonnet 43 by William Shakespeare shows how the lover feels about the absence of his beloved. He stated that the days are nights when he cannot see her while the nights are "bright days" for then, he can dream of her. This is an absurd assumption, for days cannot be nights and nights cannot be bright days in the literal sense. But when we think more deeply, we see that the speaker is talking in paradoxes to show his pain in not being able to see her during the day, for he has to open his eyes to look at insignificant things. But at night, he can see her in his dreams which is what he prefers more.
The speaker feels he is helpless in his situation of being not able to be with her or be able to see her. And even if he does, it's only in his dreams which can be torture for him, but something he prefers more than not seeing her at all.
