Answer:
I'm tall when I'm young and short when I'm old. What am I?
I'm as simple as a circle worthless as a leader; but when I follow a group their strength increases tenfold. By myself I'm practically nothing.
I walk on 4 legs in the morning, 2 legs at noon, and 3 legs at night. What am I?
I make you weak at the worst of all times. I keep you safe, I keep you fine. I make your hands sweat and your heart grow cold. I visit the weak, but seldom the bold. What am I?
I cover what's real; hide what is true, but sometimes bring out the courage in you. What am I?
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.