People are fairly simple creatures who are easily tricked because of their addiction to patterns and basic context cues. People want to trust you, like you, not need to kill you. Heck, you could be an asset to their team if you turn out to be someone they can trust, let their guard down around, and learn to lean on.
We see characters like Daryl on The Walking Dead become fan favorites both in and outside of the show while still being kind of dickish.
Stress can have extremely damaging effects on the body if not properly managed or avoided. Survival situations are hard enough without adding the chaos caused by stress.
According to the American Institute of Stress (AIS) some of the more dangerous symptoms include: Difficulty concentrating, racing thoughts, Difficulty in making decisions, Feeling overloaded or overwhelmed, Feelings of loneliness or worthlessness, Overreaction to petty annoyances, Excessive defensiveness or suspiciousness, Increased anger, frustration, hostility.