This concept is so close to my heart that it may be difficult to write about it. It's completely revolutionary for those who get it. If you don't get it, don't worry - you will with time. For those interested in reading more, I would suggest Eckhart Tolle's classic "The Power of Now" - particularly the last chapter called "Surrender".
I'm learning as I get older to welcome my difficulties, my fears, my struggles - whether it be with the guitar or with life. It's completely natural to want to avoid fear, but eventually it keeps coming back until we learn how to deal with it. Fear and limitations are great teachers.
In the practice of an instrument, we can fear fast tempos, difficult repertoire, high positions, certain fingering combinations, understanding harmony, what people think of our playing, etc. etc. Try to notice whatever it is you avoid or hide from. What do you fear? Awareness is key - most people don't know what they fear. Be curious about what you avoid in your playing and for that matter, your life. It's a fascinating study.
When you avoid something, you bring a psychological "NO" to it. It is basically the avoidance of pain. For example, if someone fears playing at fast tempos, they will avoid fast pieces and passages, they will slow down unconsciously when a fast passage appears, they might even look through a collection of music and avoid pieces with too much "black" in them. Ultimately, they are reacting to the fear of playing fast by avoiding the situation in some way. By not dealing with the fear, it is allowed to grow until "I can't play fast" is believed. Once you believe the fear, it becomes part of you.
So how do we deal with the fears and weaknesses we have? As I've learned, we must accept the fear - make friends with it. Say "YES" to what you fear - embrace it completely.
Fear can only stay strong if we keep reacting or fighting against it. If we embrace our fear, it will dissipate. This is bringing the YES into the NO.
For example, if a person fears playing fast, he or she can say "OK, I fear playing fast - that's fine. Let me play fast and I will welcome the fear. I won't complain about missing notes, tensing up, not feeling comfortable, etc. Instead, I'm going to welcome all of that and keep my mind calm. I will allow the fear to come and I will play fast anyway".
So then the person plays fast and gets tense, misses tons of notes, has a bad tone etc. However - unlike before, there is no reaction to any of this. The person keeps the mind calm and allows it all to be as it is. He or she welcomes the fear. As the fear is welcomed, it lessens because it is not strengthened through a negative reaction (the NO). This is the state of mind we want to cultivate for our difficulties. That doesn't mean you don't go back and work on the difficult passages. It doesn't mean that you ignore them. You just work on them without a negative reaction to them. You want to always say YES to your difficulties, to your fears.
With time, the fear lessens and you'll find that you can do what you used to fear. Why? Because only what you resist persists. Keep putting yourself into the situation you fear and say YES to the discomfort. As we do this again and again, the fear and discomfort will go away.
The great Eckhart Tolle talking about this concept.