Parshat Ki Tisa
Moshe comes down from Mt. Sinai and see what the people have done. He gets angry and throws and breaks the luchos. In 32:19 it says, "ויחר אף משה וישלך מידו את הלחות".
What was the big surprise? Hashem already told him what they had done - it should have been no shock to him when he came down? Why the extreme reaction? He should already have been mentally prepared for what he would see, even possibly already with a thought out plan of action!
Sometimes, often, our reactions are spontaneous. Especially when it is a reaction of anger and shock.
For example, when your child misbehaves, you might get angry and punish the kid.
More often than not, that spontaneous anger is really selfish - you feel insulted your kid acted a certain way. You feel hurt or embarrassed. If you would wait and think about it calmly you might come up with a more effective punishment.
Moshe here had time to think about it. This was not a reaction of shock and surprise. This was planned. He felt this was the most effective response in order to teach them the severity of what they had done.