Self-protection. For example:
Physical, emotional, mental, or spiritual protection—feeling you need it or fearing attack in your life somehow
Protecting your from outside influences, opinions, criticism, or judgments
An antagonistic attitude, fighting mentality, or mood of hostility
A desire to not connect with or be affect by others, the world, or specific influences in the world
Isolation
Hidden identity
Characteristics you associate with a particular character, or type of character, who wears armor (knight, warrior, etc.)
Consider also the meaning of the particular part of the body the armor or shield is protecting.