The presumption you are rebutting
Under section 214(b) of the Immigration and Nationality Act, every applicant for a temporary visa is presumed to be an intending immigrant until they demonstrate otherwise. The officer's task is to decide whether you have overcome that presumption.
This is why 'I only want to visit my sister for two weeks' is not, by itself, persuasive. The question behind every question is what will bring you back.
