Dog Eat Dog

You sit on the edge of a cliff high above when you hear the pitter patter of feet. You turn your head to catch a glimpse of one of your closest friends, you smile and turn your head back resuming to your thoughts but in an instant moment you feel the warmth of their hands on your back, sending you spiraling down to your death.
It is a scary thought isn't it? To be betrayed by someone you never expected betrayal from. To be destroyed by someone who you'd never imagine hurting. As scary as the thought may be, how likely is this to happen? We like to think that the people we love would never turn on us because we would never turn on them but isn't that like a deer expecting a lion not to eat just because the deer didn't eat the lion? Are we all not prisoners of this imperfect concept of trust?
Do people not always turn on us from time to time?
If it is not every man for himself then why does it feel like a dog eat dog world where the strings of unity are faded and worn out?