I have heard about... 

Former employees of a company later hacking them (How can we trust that they can be trusted with sensitive details?)

Most homicides involving a spouse killing the other (How can we trust people? Including loved ones?)

Stories of people secretly being sex offenders (How can we tell if they are hiding something?)

And finally, SO MANY TIMES, in those tales, people will say things like "they were such a pleasant individual in person, they could never do such a thing!"

How? How can I trust ANYBODY? I am so scared that, for example, my friends might secretly be murderers, or worse! Combined with trust being inherently a risk, I wonder how I can feel safe at all.