FOR ANYTHING (be located) - "walk under someone else" - to have a patron, protector; state of obedience, subordination; "To be under the wing" (defense), "under the table", "under the counter" (secretly), "inspired", "under the nose" (in sight). "It is under the yoke, under the yoke, under the weight of ..." - depression, loss, negative emotions.
Being underneath something suggests either taking shelter or submitting to someone else's handling of us. It may also represent the part of us that we hide, or the part that is less capable.
Below something or someone
Inferior or unworthy
Being subordinate to someone or something
Subject to an activity or process, as in "under surveillance" or "under investigation"
Covered, obscured, hidden, or secret, as in "under wraps"
More basic, or a foundation for something else