Have you ever had someone instill a seed of doubt in your mind? And then you felt the reality of your perception shift?
For instance, have you ever thought someone was wonderful until someone else said they weren't, then despite how hard you tried to remember how wonderful the other person was to you, you couldn't?
It is because you have a subconscious belief that is MATCHING the suggestion. Nothing can be internalized in your subconscious without it MATCHING a belief first and drawing it out into the conscious mind. Unless you're a child who is impressionable and open to suggestions while you're still forming your belief systems.
We can have these suggestions planted when our defenses are weakened through over exposure and boundary manipulation- that's why mass media tries every which way to break down your boundaries with subliminal messages, programming overt and covert. Once you're exposed to the message that you're not enough unless you acquire more material items over and over and over, it's way easier to get you to buy something!