I used to trust my wife, we had been married for 20 years, then one day I came home and she was fucking the mailman, since I can't trust her anymore she has to wear a tracking device at all times.
The scorpion promised not to sting the donkey in the back while crossing the river. The donkey trusted the scorpion.
Guess what happened.
The donkey died from poison, and the scorpion drowned.
means that you are weak and can't just think what you want. no one in this world is trustworthy. Trusting someone is pretty much telling them that they can do whatever they want and you will not question them.
GUY: "Babe, you don't trust me?"
GIRL: "Yes I do. I trust you with all of my heart."
Now he can cheat on her and keep saying "you trust me, i wouldn't do that to you."