Which one of these two is correct? Is it necessary to write 'you are' instead of only 'you'?
Both are correct, replace the verb 'am' (which is current tense version of the verb 'be' as in 'to be') and you can see the structure better.
I am better than you.
I dance better than you.
I am better than you are.
I dance better than you dance.
If you write 'you are' then you are emphasizing it and nothing else.
So grammatically both are correct.
- Virat is a better batsman than Suresh.
- Virat is a way better batsman than Suresh is.
- I got more brains than you.
- I got more brains than you do.
In a sentence with "I" vs. "you," I can see where adding or subtracting the "do" is a matter of style choice.
But in the sentence "Nobody knows your life better than you" there is room for ambiguity.
Without adding the "do," the meaning might also become "Nobody knows your life better than (they know) you."
Adding the "do," it becomes clearer that the meaning is "Nobody knows your life better than you (know your life) do."