William Ernest Henley

In the fell clutch of circumstance, I have not winced nor cried aloud: Under the bludgeoning of chance my head is bloody, but unbowed.

English Poet

Use 'unbowed' to describe someone who remains strong and determined, not discouraged, after setbacks.

Steadfast Spirit

'Unbowed' is often used in situations that are intense or dramatic where resilience is shown.

Dramatic Situations

The term doesn't only refer to physical challenges; it can also mean staying true to beliefs or principles.

Not Just Physical

 A good scientific law is a finely-tuned machine, accomplishing its task brilliantly but ignorant of why it works as well as it does. A good scientific theory is a bruised, but unbowed, fighter