The lesson is don't inappropriately wield a gun in a tense situation.
Watch the New York Times video I posted a few pages back. The video is shot from behind the McMichael truck. Arbery was running toward the back of the truck. The view of when Arbery first grabbed the gun is blocked by the truck. Travis was on the left of the truck, and Arbery ran from the back around the right side. It appears that Arbery charged around the front of the truck after that in an attempt to seize the gun. Then he started punching Travis, who outwrestled him for control of the gun and shot him twice.
The judge excluded evidence of other encounters with police and other people where Arbery had done the same aggressive grabbing thing. That's going to be a strong basis for appeal if the jury votes to convict. His probation also probably had an effect on how he acted.