I am experiencing a weird problem that makes my performance in OI contests very bad. I can't identify easy problems, and I usually over-estimate them and ignore them and try in other harder problems, and even when I don't ignore them I don't have the mind to solve a problem rather than collecting points from subtasks.

I have seen this pattern in so many OI contest I participated in, I usually solve some harder problem while the easier one holds my score back, especially if those easy ones requires some greedy approach or some observation. Is there a way to avoid this situation rather than solving hundreds of these problems? I'm totally OK with solving some, but I have to practice on hard problems too. Does anybody experience this situation before? How did you get over it?