Wrap your mind around

When you're trying to 'wrap your mind around' something, it means you're trying to make sense of something that is really sad, unexpected or shocking that takes you by surprise and doesn't make sense.

Example:
-I can't believe Kyle was killed in a freak car accident.
-I know. I just can't wrap my mind around it. So tragic.

Just up and

'Just up and' used between a subject and verb means that someone did something suddenly, without warning. It usually involves a big change in life.

Example:
-What happened?
-Well, he just up and decided he wanted a divorce.
-What was her reaction?
-She was dumbfounded.