Tacit knowledge is the knowledge in our heads. Also, our hearts and hands, but that is another matter. It is that which we know. We carry it with us.
We gain tacit knowledge in a number of ways. Experience is the most significant source, but experience alone is quite insufficient. We need to understand relationships as presented by others either in person or in some documented form. Knowledge is present in frames of understanding, also referred to as schemas. A frame is a situation. We arrive in a situation through a path of other situations. Each frame must be recognized to fully appreciate the frame or situation it leads us to.
An expert has been shown to be someone endowed with tacit knowledge of immense proportions. Where a lay person may see a tree, an expert sees a forest, with a highly developed, highly nuanced combination of options and alternatives that others could not even imagine. The expert, through desire, effort, study, association with other experts, and natural talent, has the capacity to see beyond what others see, to conceptualize outcomes from a much broader base, and to integrate frames of knowledge at a breathtaking pace.
Such knowledge is a precious resource. Extending it for the good of all is a critical task, one destined for our times.