same thing happened last year where they started pretty good throughout the first half of the season but failed in the end to maintain a qualifying spot for the champions league, but this year could be different since we see Atletico Madrid, Barcelona doing bad this season, Sociedad could make it and qualify this year, they have good chances to be in top 4.
If you see Atletico Madrid giving a bad performance again, it is likely that together with Barcelona will be eliminated first before getting into the top 4 which they expect sooner. Seeing that Sociedad's position is also actually threatened for Real Madrid, followed by a slight difference, and of course it hasn't made it safe in the standings now.
I didn't think that Real Sociedad could show such aggressive performance in every match. In fact they are consistent to stay afloat.