What is Brian's most important discovery in Hatchet?

Without a doubt, Brian's most important discovery during his whole ordeal is his ability to make fire. Not only does his ability to start a fire save him from dying in the wilderness, it allows him to thrive.

While there are a number of benefits to having a fire near his shelter, including warding away mosquitoes and nighttime predators and staying warm and dry during poor weather, the greatest benefit from the fire is the...

Without a doubt, Brian's most important discovery during his whole ordeal is his ability to make fire. Not only does his ability to start a fire save him from dying in the wilderness, it allows him to thrive.

While there are a number of benefits to having a fire near his shelter, including warding away mosquitoes and nighttime predators and staying warm and dry during poor weather, the greatest benefit from the fire is the ability to cook food.

The human brain consumes an enormous amount of energy, and the only efficient way for humans to consume and process enough calories in one day is to cook our food before eating it. Brian would not have survived for very long if he had to forage for plant matter and eat it raw. Cooking plant matter and meat gives him the energy he needs to improve his living conditions and eventually escape.

I strongly recommend viewing the following video from PBS, which discusses the importance of cooking from an evolutionary and survival perspective: Why Do We Cook?.