Is being too similar bad for a relationship?

Then a study in 2009 found that couples higher in marital satisfaction were more similar in their personality and attitudes (Saltz, Gail). So this research does suggest that if you are with someone who is very similar to you, you will have a more successful relationship.

Why do similar people not get along?

When two people cant get along because their personalities are too similar, thats also a personality clash or perhaps a power struggle. It is common to say, they are too much alike, with the implication that the similarity causes the clash.