It's a natural thing for humans, for all animals for that matter, to put a lot of stock in their first impressions. It's not entirely surprising; sometimes life and death is decided in only a few seconds. The deer decides whether to stay still or run from the wolf, as does the antelope from the cheetah, even humans have fight or flight responses; they all depend on the first impression.
In the month of April I played four games in particular after the excellence that was Mass Effect 3; The Old Republic, Witcher 2, Tera, and Diablo III. Every game came up wanting for one reason or another; Republics' story wasn't as deep, Witcher 2's combat was a tad wonky, Tera's story was non-existent, and Diablo III was just a shade weaker than expected. Those were all my first impressions. Then came Guild Wars 2, a game lauded for its combat, and I was unimpressed. I found it wanting versus the brilliance of Tera's combat and it made me pause. Earlier in the week I had been sure that I wasn't going to play Tera based on the fact that other than its combat I was bored, sure it doesn't do anything wrong but it didn't feel like it would be enough. When I went to play the Guild Wars 2 beta I realized that my first impression of the game, while not complimentary shouldn't be enough to stop me from playing some more, in this I realized that I had to give Tera more time to pass or fail.