Do you think it's possible to 'not be cut out' for monogamy?

Remaining completely neutral, I want to ask the following question: do you think that open relationships exist because people genuinely can’t be monogamous, or do you think this permission to say that one can’t be monogamous is simply:

a] a post-modern construct

b] for people with emotional / psychological issues not healthy enough to be in a committed relationship (i.e. sex addicts, afraid of intimacy, etc…)

Or do you think open relationships are legitimate ways for people to explore their sexuality without being limited.

My own opinion, once again, remains neutral.