Boiling the ocean for a cup of tea.

Here's something to contemplate about. Let me make clear the scenario . You have a ocean and you need a cup of tea. Assuming the salinity does not count, would you first simmer the whole ocean and take a cup from it , or would you take a cup full of water and heat it to make the stained drink. It is a no brainer, I recon ..But then why are we trying to change the whole world at one go?