Guys, Why do men exaggerate their sexual abilities?

I had a guy hype up his sexual ability through messages, talking about what he'd do, and was so excited. We had sex (in nature so I'll give him some slack) and he underperformed from what he said. He seemed nervous or awkward as well. Leading up to and after. It was so weird.

Guys, Why do men exaggerate their sexual abilities?
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