坚不可摧

• 不(no; not; negation)ASSOCIATIVE

A bird flying swiftly upward and never willing to return represents the meaning of swift and unyielding.

• 口(mouth; opening)RADICAL
• 丁(man; adult male)PHONETIC

A mouth uttering words of approval with a sound like "ding" gives you the character meaning "can" or "able."