Dwarves are born with a bone-deep knowledge of their One, but Thorin stops feeling the pull of his after the dragon attacks Erebor. Needless to say, he is surprised, and not initially pleased, to find his One living behind a round green door decades later.
Hobbits find a seed that represents their innermost self and can offer it to someone else to plant. This creates a bond as strong as deep roots in the earth between them. It is just like Bilbo, after years of thinking that no one would want his, to offer his soul-seed to a dwarf that does not understand gardening metaphors.
But just because they have found each other does not make the quest to reclaim Erebor any easier, and in the end a sacrifice is still made.
Thorin has to trust in the strength of the bond between himself and his One, because otherwise he will never believe that the sacrifice was worth it.