Looking at the pattern so far, my opponent has chosen scissors twice (rounds 1 and 3) and paper once (round 2). Since they just played scissors in the previous round and we tied, there's a reasonable chance they might stick with scissors again. Players often repeat moves after a tie. By choosing rock, I can potentially counter scissors if they repeat it. Additionally, I'm currently behind in score, so I need to start winning rounds to catch up, and this seems like a strategic opportunity.