"Mud" shows up in a variety of forms, especially in our relationships with each other. Used properly, it can help us grow our personal power and inner strength, our conscious awareness and ability to love. This attainment is an inner journey, and our experiences, especially the muddy ones, are the path to that growth.
 
Let me explain with an analogy.
 
Everyone has to learn, one way or another, that fire is hot and it burns. No matter what a child is told by mom or dad, when he/she finally and truly learns about fire, it is usually through direct experience. That experience then creates understanding, and eventually, wisdom.
 
Our understanding is based either in fear or love. Fear can cause the child to avoid fire altogether, and love (or respect, an aspect of love) can guide the child to learn its proper usage. One who avoids the fire out of fear is in servitude to it; there is no power or higher awareness. One who learns to use it achieves dominion over it, which gives him/her the wisdom to move forward powerfully in life.
 
Now, map this on to your experience in relationships. Have you ever felt "burned" by a relationship? What did you do about that? Chances are this was to be a direct learning experience intended to teach you about yourself, to open your eyes to new awareness and understanding. Did you gain love and wisdom, or did you learn distrust and fear?
 
We are enslaved by our relationships if we avoid them (or any aspect of them) out of fear. We have true power if we use them as a training ground for higher awareness -- to learn about ourselves and others, to learn the how they work, to learn to love.
 
Eckhardt Tolle says that frustration is built into the human experience. It's there for our development. We see this astrologically, too. For example, Pluto and Saturn are teacher planets whose focus is soul growth through restriction, intensity, and challenging (sometimes painful) situations. Those experiences help highlight incorrect concepts (ideas, beliefs, thought processes) that need to be dissolved and to teach new, more empowering concepts.
 
This process can seem harsh. Sometimes we feel punished or persecuted by someone or some situation. It's when we relate to our life as "it shouldn't be this way" that we suffer. In other words, pain occurs because our perception is distorted.
 
Once you realized the purpose of The Mud, you can begin to bring heart to every situation, and rather than avoiding, go into it with the intention of getting something out of it.