An analogy or a fallacy

Fake friends don't always stab you in the back so I'm assuming you're using a biased sample to make the conclusion that they would. As far as the analogy, that's a big stretch from a ball hitting another ball as being the same as a fake friend turning on you. I'm sure if my imagination stretches with some help I might see the correlation, right now I'm having trouble because Newtowns cradle seems merely a representation of transferring energy from an object to others via momentum., not sure how that's stabbing in the back.