I used to think like teacher. I have changed my assumptions.

1) The unexpected is going to happen.
2) I am going to get hurt.
3) I am going to get lost.
4) I am going to spend the night in the woods.
...

Even if you are only going out for a few hours when the weather is nice. I think being prepared to spend the night in the woods while it is cold/raining/snowing is smart.

Just remember Murphy's law.