Something indomitable can't be beat. People described as having indomitable spirits don't need pep talks or protein shakes; their strength comes from within.
The adjective indomitable starts with the Latin prefix in, which means "not." The second part of the word is also from the Latin word domitare, meaning "to tame." So the word literally means "not able to be tamed." Indomitable is often teamed with the words spirit or personality to describe someone with a can-do attitude.