The basic meaning of overhead is "above one's head"
However, in business field, usually An overhead cost or expense. ‘overheads, such as lighting, equipment, and any little extras, are paid for out of a centralized fund’ Overhead (business) - WikipediaOverhead (business) - Wikipedia
In computing field, In computer science, overhead is any combination of excess or indirect computation time, memory, bandwidth, or other resources that are required to perform a specific task.Overhead (computing) - Wikipedia
So the key extending meaning is 'indirect and excess'.
I really unable to relate the meaning to "above one's head"? What can I discern might be 'dangerous', 'pressing', 'important' above one's head?
Is there a fable or a proverb about this?