In the face of adversity, he remained unshakeably steadfast.
Tips
memory
坚 (firm / solid) + 忍 (endure). Firm endurance - the exact picture of "tenacity".
usage
Formal. Often in the set phrase 坚忍不拔 (steadfast and immovable). Don't confuse with 坚韧 (jiānrèn, "tough and flexible") which emphasizes resilience of material or will.
