Imagine a couple having a troubled relationship. Imagine that both of them approach you and tell their story. They talk about how their partner is troubling them and despite all the effort they make; their partner is not allowing the relationship to grow. You will hear accusations from both the sides and most of them will sound very convincing. But both parties cannot be right in their blames. The truth will lie somewhere in between.
When a couple approaches you with a problem, you act as an observer and listen and think without any emotional input. When the problem arises in your own relationship, you somehow become one-sided. You only look at the situation from your perspective and give no notice to what your partner may be thinking. That makes it difficult for you to understand the real cause of the problem and its cure.
Once you realize that you may also be at fault and agree to do self-introspection, you may reach the core of the problem quickly. For that, you need to keep your emotions and hurts aside and think neutrally. Once you look at your own faults, you can do something about them. At least one side improves upon its faults by this. For a relationship to survive and thrive, self-introspection and analysis is necessary. Put yourself in the other's shoes and think about the issues. The answers will reveal themselves fast.