"Even the smallest person can change the course of the future." – Galadriel; In an attempt to get the Arkenstone back for Thorin, Bilbo discovers the ring he's been using is the One Ring. Seized by a need to destroy gold, especially gold with the ability to ensnare creature and king alike, he sets out alone for Mordor. Anything to forget about the love that gold cost him. What he doesn't know is that Thorin is no longer under the thrall of gold, and is desperately racing to catch up with him to keep him safe. They may have just started on another adventure, but this one may not end as well as their first quest.
By a curse or a blessing from the Valar, Bilbo finds himself repeating the same horrific day of war outside of Erebor again and again. His repeats are always triggered when someone from the company falls. He suffers days and days on his own before the others begin to repeat the day with him.
One would think that with the whole company, an elf king, and a bowman all knowing what was to come, Bilbo would have an easier time getting them all through the day alive.
One would think that, wouldn't they.