Musicianship includes at least three aspects. They are technique, theory, and taste. A grasp of these three areas will provide the foundation necessary for anyone to become a well-rounded musician. You could have excellent technique, but poor taste and your ideas will be well executed and poorly received. You could excel in music theory yet have poor technique. You will then be unable to produce the sounds you can construct on paper. A well-rounded musician is growing in the areas of technique, theory, and taste.
Technique is mastery of the building blocks of a style. Technique has to do with your hands; it is a physical skill. It is the ability to play the music set before you. Musical technique is developed by practicing scales, riffs, strum patterns, or vocal exercises. Developing technique can be tedious work and so it is often neglected. Technique is developed through practice.
Theory means understanding how music works. Theory has to do with your head; it is a mental skill. It is the ability to recognize patterns, ratios, and sequences. Technique means you know how to get from one note, chord, or phrase to the next. Theory means you know why you are going to the next note, chord, or sequence. Knowledge of theory is developed through reading and instruction.
Taste means knowing what fits. Taste has to do with your heart; it is an emotional skill. It is the ability to recognize what is appropriate in a particular context. It has to do with dynamics, phrasing, and articulation. While technique and theory inform us as to what to play and why we play it, taste informs us what not to play. It is recognizing that silence can be the most important note I play. Taste is developed by listening attentively to music to recognize what the musicians are and are not doing.
Becoming a well rounded musician means developing in all three areas of technique, theory, and taste. Someone who is moderately developed in all three areas will ultimately be of greater use than someone who excels in just one or another area. Musicianship is not something you are either born with or you are not. It can be developed by focusing on developing technique, theory, and taste.