Intuition behind a cournot duopoly nash equilibrium producing a higher output than a monopoly?

Question

I am just wondering if someone could explain the descriptive, not mathematical intuition behind why a cournot equilibrium for a duopoly produces a higher level of output than a monopolist but lower level of output than a perfectly competitive maket?

I can understand why a cournot model with many firms would result in a perfectly competitive outcome but why would a duopoly necessarily result in a more efficient outcome than a monopoly?

Thanks in advance

Answer 1

Producing more will decrease the price and therefore the profit per unit sold. For a monopolist, all units are their own units. For a duopolist, many units will be the competitor's units.

Viewed differently, producing more produces an externality between producers via prices in a duopoly. A monopolist internalizes these externalities completely.