When we evaluate the people we're seeing as potential life partners, we tend to consider of the pros and cons associated with dating them. Pro: Nice and caring. Con: Doesn't like dogs.
According to a recent study published in the Personality and Social Psychology Bulletin, most people actually tend to focus more on their partner's negatives, or "deal breakers," rather than the positives. Those negatives can include an annoying personality trait, their religious/political beliefs, etc. What's interesting about evaluating these deal breakers is that they're different for everyone: while someone might find shyness endearing, another might find it frustrating.
The study's conclusion was that people evaluating potential relationships tend to focus more on deal breakers, so much so that a few negative traits could totally override a number of positive traits. They also found that women focused more on the negatives in general. Ultimately, this means that we may sacrifice partners who are largely compatible with us because we place too much importance on negative traits.