Frodo is being consumed by the ring and his mind is occupied with the larger
fears of entering Mordor and how he is to complete his mission. Sam is
left to deal with the lesser, but more immediate dangers such as Gollum.
The two complement each other well and Frodo needs someone to ground him back
in the day to day reality of the journey rather than its cosmological
end. Call it cosmic sense versus common sense with the two
hobbits.
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"All wizards should have a hobbit or two in their care..."
