When we are discreet, we are careful not be be to obvious and do things in a quiet and tasteful manner. It does not mean that we are nervous, afraid or suspicious. If I keep a secret, I am being discreet. If we are wary, we are careful, but also suspicious and alert for possible problems - also, possibly a bit nervous. If I am in a neighborhood that I know has a lot of crime, I am wary, not discreet.