The main determinant of whether we see the glass as half-full or half-empty is our personality, specifically whether we are of an optimistic or a realistic disposition. Optimists view the future as free from significant risk and full of opportunity. Realists are aware this is not the case, and that there are potential for various problems, foreseeable and unforseeable. 

Optimists tend to have better stress levels, health and interpersonal relations. They're easier to be around. They make good entertainers, salesmen, politicians, entrepreneurs and CEOs, but are blind to risk.  They seek out opportity and externalize failure. Trump is an optimist (and narcissist).

Realists worry and fret and plan, with a focus on averting disaster. They carry stress and can be hard to be around.  They are often the bearers of bad news. They make good lawyers, doctors, accountants and engineers. Obama is more of a realist.

Both temperments offer strengths or weaknesses, depending on the task at hand.