How do people manage to play Rock, Paper, Scissors so quickly?

Don't get me wrong, I totally understand the rules of the game, its rather simple. My question is how do people manage to play out 3 rounds in less than 5 seconds?

For me, it's a multi-step mental challenge that would take me like 15 to 20 seconds slowed down to complete.

• • Pick a word, Rock, Paper, Scissors
• • Remember how to shape my hand
• • Punch Rock into my palm a couple times anyways, as apparently Rock is the default before the actual sign is thrown
• • Remind myself how to arrange my own hand sign when the round is up
• • Observe the opponent's sign, which is only presented for about a half of a second
• ?. Oh fuck, I didn't have enough time to register the opponent's hand sign
• • Feel like a fucking idiot and walk away

Seriously, how is this game played so quickly? Is it more suitable for people that know sign language or something?