机不可失，失不再来

• 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."

• 一(one; first time)ASSOCIATIVE
• 冉(slow; soft)PHONETIC

Do it again and again, repeating endlessly.

• 木(tree; plant; stick)ASSOCIATIVE
• 从(follow; accompany)ASSOCIATIVE

Wheat (a plant with a person beneath it) is something people bring, so this character means 'to come' or 'to arrive'.