With modern technology and internet, the question has become: Is it enough to look up your opponent in the chess databases?
Going beyond that and googling/youtubing his opponent, IM Gretarsson would have found out that WGM Sopiko Guramishvili might have a thing for the Slav, well at least according to the above screenshot from a YouTube video!
Here is the combination Sopiko played after early mistakes out of theory by Gretarsson
Gretarsson,Hjorvar Steinn (2509) – Guramishvili,Sopiko (2414)
22…Bxf2+! 23.Kxf2 Rd4! and because 24.Qc2 Ng4+ 25…Qxg3 is killing, White gave his queen with 24.Qxd4 but lost anyway.