Why can't I feel the effects of kava?

Could you elaborate on why some individuals may not feel the intended effects of kava, despite its reputed relaxing and anxiety-reducing properties? Is it due to individual physiological differences? Could there be a possibility of tolerance build-up, particularly among frequent users? Or perhaps the quality and preparation method of the kava itself might be a factor? I'm curious to understand the potential reasons behind this lack of perceived effects, and whether there are any strategies or adjustments that could potentially enhance the desired outcomes.