Humans are biological machines run by their subconscious. Learn why you do things, feel a certain way or think things. Understand if it’s serving you and reprogram it
It’s the job of the communicator to make sure the person they’re communicating with understands. Not the other way around. If they didn’t understand it’s not their fault
People will say they understand and if it’s important always ask them a few questions to confirm. They will say and think they understand, but actually don't comprehend what you were trying to communicate
