1. (archaic): Lacking confidence in others; distrustful.
2. Lacking confidence in one's self; distrustful of one's own powers; not self-reliant; timid; modest; bashful; characterized by modest reserve.
"Man, Robert lacks confidence in others and is so distrustful."
Y'know, there's a word for that. It's called diffident.
"Man, Robert is so diffident."
Now you're learning.