I thought it took a deeper level of understanding...
Well, it's not rocket science. But you do need to have a good understanding of ratio.
There is a rule-of-thumb starting point in portraiture. For general portaits, begin with a 3:1 ratio. When photographing older people (old enough to have wrinkles), consider something less, like 2:1
A more dramatic setting might call for 4:1
Remember... photography is making a record of reflected (sometimes transmitted) light. It follows: no light, no record.
To communicate in two dimensions a three dimensional scene, highlights and shadow are necessary. In order to record detail in shadow areas, they must be illuminated. For the purpose of this discussion, lets consider the amount of light illuminating the shadows as one "unit" of light. If the light falling on the highlight side of the subject equals one unit of light, the scene appears "flat." If we increase the light on the highlight side to two units (a 2:1 ratio) we begin to see shape communicated.
With this in mind, if we light a subject with a unit of light that illuminates both sides [we call this a "fill" light] and then add a light twice as bright (two units) to just one side of the subject [this is called a main light or key light], the results are a 3:1 ratio since we added the two units of the main light to the one unit already provided by the fill light.
Since you are not currently creating your lighting ratio, you will have to learn to see ratio in existing light and then measure it to make adjustments using reflectors or go-betweens (gobos).
I hope this helps.
-Pete