In each of these senses, fine qualities are sought that can easily be 'overlooked'. The cultivation of these qualities ensures a deep internalization of the instrument and has the potential to take your own play to a higher level.
The fourth principle refers to a special approach in the development of a piece.

Physically speaking, a tactile fusion with the instrument is created when the energy coming from the body can flow into the instrument without disturbances or disruptions via the points of contact.

An optimal power transmission is expressed in the feeling of a 'rich' tactile connection to the instrument. It offers you the highest level of security and information in the development and management of difficult passages. So at the points of contact, you ensure a permanent, 'rich' well-being.

Experiment with the conscious variation of the overtone spectrum by changing your way of playing and look for a sound quality that you like.

Such a concentration, directed at the sound quality, promotes an extremely enjoyable merge in the self-generated sounds. It can make 'high' when used consistently and is able to carry the entire practice process.

Pay attention to your body! Your body signals you a strained movement by a subtle contraction. So for a technically difficult passage, you will first have to find a simplification with which you can execute this passage without the feeling of contraction.

With growing security, the desire arises spontaneously and from the inside to go ever closer to the original version, i.e. to push the limit of what you can master in the feeling of effortlessness further and further.

Play around improvising with the notes of the studied piece. Note values, slurs and dynamic signs do not have to be observed yet. First, convert the music into optimally sounding notes and pay attention to the dense and 'coherent' contact with the instrument and the sound produced. Immediately improve what you notice disturbingly!

Be sure to consistently make this search for quality in the tactile sense, hearing and feeling in a musical kind of way! Without this musical approach, there is no flow, no creativity, you get 'stuck in practising'. Your musicality is the fuel that drives you to the desired final version of your piece in a self-organized process guided by your senses.