Question

On Thursday evening you explained that the rule “the one who seeks to take from another bears the burden of proof” is based on the presumption that whatever is in a person's possession is his, and that this presumption is not a statistical principle (that there is a greater chance the object belongs to the one in whose possession it is, because most objects in the world belong to those who possess them), but rather an efficient legal principle (the chance that it belongs to the defendant is 50%, except that nothing can be done other than requiring the plaintiff to bring proof; otherwise anyone in the world could make claims against someone else). 
 
What is the law in a city where 90% are robbers? Would we still say there, “the one who seeks to take from another bears the burden of proof”? Would we still say there that the chance that the object belongs to the defendant is the same as the chance that it belongs to the plaintiff (50%)? 
I assume this would not be said, and if so, we see that ownership of the object depends on the probability of what exists in the world, not on what exists in court.