live by/on (one's) wits
To survive or make a living through one's intellect and resourcefulness. When I lost everything, I had to live by my wits, and it made me a stronger, more savvy person.
live by one's wits
Fig. to survive by being clever. When you're in the kind of business I'm in, you have to live by your wits. John was orphaned at the age of ten and grew up living by his wits.