As·ser·tion (ə-sûr′shən)n.1. The act of asserting.2. Something declared or stated positively, often with no support or attempt at <span>proof.</span>
This words simply means not easily convinced. Or even having doubts.
Macbeth thinks Malcolm cannot harm him, because of the witches' prophecy. The witches' prophecy stated that any man born under a woman cannot hurt him.
A bias because subjective deals with ones person opinions. Objective deals with facts <span />