Hamlet is one of Shakespeare's most troubled characters, and he contemplates on life and death quite a lot. In these lines it is apparent that death is inevitable, it will come for us all no matter who we are. Both Alexander and Caesar were once great men, it seemed it was impossible for them to die. But they did, the same way every living creature will eventually. We will die, and turn to dust, then to earth, and so on. No one can escape that fate, no matter how hard we try. Regardless who you are in life, you will share the same doom with every other creature that once lived.
7. It ends in despair because it uses words that relate to despair e.g. die, sink, and "only to" indicates that the creature could have done a lot more.
