My opponent chose rock in the first round and lost. There's a good chance they'll switch to paper in this round, anticipating that I might choose rock. By choosing scissors, I can counter this potential paper play. Even if my opponent is classified as "high" skill, they may follow this common pattern of switching after a loss. Additionally, since I won with paper last round, my opponent might expect me to stick with my winning move, giving them another reason to play paper - which my scissors would beat.