Understanding stems from natural human experience. Some kinds of natural experience:
These experiences are holistic, engaging our minds and bodies, and are usually physical in nature.
Many of the metaphors found in language are derived from these natural forms of experience. This book (Metaphors We Live By) spends a good deal of time mapping these relationships.
Many things we encounter on a day-to-day basis have no "natural experience." Finance, computers, political structures, buildings, etc. We use metaphors to get a grasp on these ideas, to articulate aspects of them to both ourselves and others.