9. Lack of effort
Relationships usually require work. There are always decisions to be made and compromises to reach. Successful couples are not selfish and realize that they both have to give in from time to time to make things work. Partners who find themselves in the position of always having to be the one to give in to please the other could be up against a relationship killer that will eventually bring things to an end.
Partners who really care about the relationship will be willing to sacrifice their wants and desires to please their partner some of the time. Be cautious of score-keeping however, as that can lead to feelings of animosity over the notion that one partner is working harder on the relationship than the other.