Bilbo gives away the Arkenstone
During the siege of the Lonely Mountain, Bilbo secretly carries the Arkenstone, Thorin's most coveted heirloom, to the besieging Elves and Men so they can bargain with it and a war can be avoided. He then walks back into the mountain to face Thorin's rage, even though he knows he has betrayed his employer's greed. It is a concrete case of a low-status member breaking with his own side's leader to stop a disaster that stubbornness was causing, and accepting the personal cost.
