We need to identify the Useful God Yong Shen 用神 for our BaZi Four Pillars of Destiny, and preferably the Useful God needs to be produced by the BaZi Four Pillars of Destiny itself. If we decided that Fire is the most needed element and Fire was identified the Useful God, but if Fire is not available in the basic BaZi Four Pillars (the 8 characters), then if we were to encounter Fire through any Ta Yun The Ten Years Luck Pillar or even in any year, month, day or hour Pillar, this Fire is to be precised not considered as Useful God 用神 or it is short lived.
We need then accept that any Fire can but function as one of favorable elements, its influence perhaps notable but short-lived. Remember Ta Yun last for ten years.
It is very fortunate when the Useful God is found in our BaZi chart, but we have to bear in minds that merely finding the Useful God available in the basic structure may in itself be not sufficient, without also assessing its strength, health and position. Strength and vitality of the elements in a chart are then decided by time (season, i.e. month of birth, but also hour of birth), location (where in the chart do we locate the element) and environment (e.g. Daymaster or Useful God being otherwise sustained by other elements in the chart). Function and availability of the elements in a chart will be then further decided by vicinity, if the element is clashed away or being taken away by combination, transformed into other element, or supported or under control.
If Fire is identified as your Useful God, but fire is missing or very weak with no support in your BaZi, then Fire becomes somewhat not functional in an astrological sense. Then we might consider choosing the next favorable element that we find available in the structure. However the auspicious is not as strong as the most desirable element and you may find that this can then not render the same effect for a life as would be true for a Useful God.
In short our Useful God 用神 ‘Yong Shen’ must be strong, healthy, to be produced, well positioned and well protected in our BaZi Four Pillars of Destiny. If not, we need to wait for the right timing the Ta Yun your Ten Years Luck Cycle.
Again, balance in a chart may not be taken to mean that all Five Transformations are equally present in a Four Pillars structure, as balance should be much more understood as a situation by which all favorable elements appear in the structure and are readily available in relation to their position and strength.