The glass analogy is not helpful. A half-full glass might even threaten your life.
Talk about optimism and most people will think of the glass analogy. But what does having a half-full glass really mean?
Let's say your presentation bombs, the boss criticises your work or you say something really embarrassing.
Who is in your ear? Is it a supportive friend reassuring you, or a contemptuous critic shouting, 'How could you be so stupid?'