The Course talks about the development of trust. What is that?
Well, at first you trust the ego and its false truth. You don't trust God, and you don't trust the real truth. You have trust, it's just misplaced.
Trust is the same thing as faith which means, that you learn over time that God's truth is true and the ego's truth is not true. Also you learn that God's truth can be trusted, and you come to learn that the ego that you used to trust is actually not trustworthy.
The ego's trust is based on you being unaware of its motives and the side-effects of believing in it. It wants you to think its your friend. It wants you to think it is cohesive and makes sense and is sane. It doesn't want you to see the ways in which it does stuff which undermines its trustworthiness.
While the ego has the wool pulled over your eyes you will trust it. You'll trust everything about it. You'll trust your senses. You'll trust the idea that you are a physical body. You'll trust your body's senses, your memory, your perceptions. You'll trust that the world is really happening.
But these are in fact forms of mis-trust in God, because to have so-called trust in illusions is to not trust at all.
Learning to trust God means that you become convinced that God's way is the truth, that you can depend on it, that you rely on it, and that you want it. And that HAS to entail you relinquishing your trust in the ego's version of reality.
You have to to unlearn the trust you've placed in the ego in order to reveal the trustworthiness of God.
God can be trusted because God is love and wants only to love and support you. The ego can't be trusted because it is the anti-christ and would like you to cooperate with its plan of death. It's a slight difference.
As you gain trust in God's truth, you begin to seriously question trusting the ego's world. And that means when the ego makes shit happen you have trust in God moreso than the appearance of what's happening. You trust God more than events suggest you should. You ignore what the ego is screaming at you through all your senses, and listen within instead. That's having faith. Faith is trust.
It's safe to trust God.