This is a guide to this movie. Some people obiously need to take "How to follow a simple storyline" classes.

The guy dressed in black is a thief.
Why is he a thief?
because he need money.
Why does he need money?
He doesn't have any.
Why doesn't he have any?
Because during class he either counted the black dots on the seiling, or dreamed about moonpies and pennywhistles.
Really?
Yes.
What was a robber doing at a museum?
He wanted to steal a diamond.
Why didn't he rob a bank?
He tried, but turned out he didn't have a credit card. So he applied for one, but they denied his application.
Who are the blue guys?
Guards.
Why were they blue?
Police are usually represented in blue or black, since my main guy was black, I felt you guys would be confused enough.
How did he climb the wall?
Use your imagination. Maybe the wall was perfectly smooth and he had suction cups. Or maybe it was so rough that he was able to climb it. I can climb the the corner of my house.
Why did he climb the wall?
To get to the roof.
Who were the blue guys on the rooftop?
Security guards.
Who was the guy in black?
The thief.
Wait is it the same guy who climbed the wall?
You bet.
Why did he kill all the guards?
Otherwise they would've kiled him. They started shooting first.
Why did he go to the roof?
To get access to the vault with the diamond.
How did he get down to the vault?
He was suspended on a rope.
Why didn't he turn off the alarm?
Due to the warnings. Maybe it is a trap for thieves. If you turn it off the whole building explodes. But the diamonds will be fine. Only a diamond can cut a diamond.
Why did he disreguard the "Do not steal the jewl" sign?
Did you see him reading that sign? Neither did I.
I hope this guide will help you understand my super complicated storyline.