The opponent has used scissors in two rounds (rounds 2 and 7), winning with it most recently. Since they just won with scissors against my paper, they might continue with scissors expecting me to stay with paper, or they might anticipate I'll switch to rock and choose paper instead. I'm selecting rock as it breaks my recent pattern and could potentially counter if they use scissors again. Additionally, rock has worked well for me earlier in the game (winning in round 2).