Since my opponent chose paper in round 1, there's a possibility they might stick with paper again, as players sometimes repeat successful moves. Alternatively, they might anticipate me switching to paper (to counter their previous rock) and choose scissors. By choosing scissors now, I can win if they repeat paper, and tie if they also switch to scissors. This is a calculated risk based on limited information from just one previous round, but scissors gives me a reasonable chance to counter their potential strategy.