What does the death of Curly teach Buck in The Call of the Wild?

When Curly dies, Buck gets his second important lesson in
how to survive in this wilder environment that he has been put
in.

When Curly dies, it is because she was knocked off her
feet.  Once she was down, all the dogs of the pack jumped on her and she was soon
dead.

So what Buck learns from that is a pretty obvious
lesson, right?  That dog died when she got knocked down, so don't get
knocked off your feet when you are in a
fight.

This lesson will come in handy later,
especially when Buck fights Spitz for control of the team.