Frodo Baggins' journey in The Lord of the Rings is undoubtedly heroic. Taking up the mantle to carry the One Ring, the very weapon that could change the tide of war, and ensure its destruction is no small task. However, according to Joseph Cambell, the author who coined the story structure of a hero's journey, it's Frodo's own heroic quest that prevents him from having a typical hero's journey. The hero's journey is typically made up of twelve steps broken into three acts. The call to adventure, crossing the threshold and the ordeal are a few steps in a standard hero's journey. However, the One Ring uproots Frodo's journey with its very existence.
The Ring's power of temptation, semi-sentience, coupled with its determination to return to Sauron is the wild card. Being able to tempt not only the bearer but also the people around it, the Ring carefully ensures that it gets to where it wants to be. This means driving Frodo down the path that it wants him to go. That path winds up being an unorthodox hero's journey.
Frodo's Journey Has a Standard Heroic Start
Frodo is introduced to the audience in a typical fashion. He is living his peaceful life in the Shire with his uncle Bilbo. With Gandalf realizing that Bilbo is in possession of the Ring and advising him to leave it to Frodo, everything is set for Frodo to begin his journey. Gandalf urging Frodo to take the Ring to Elrond is Frodo's "call to adventure," and Frodo's attempt to give the Ring to Gandalf is his "refusal to the call." Of course, Gandalf convinces Frodo to go anyway with the reasoning that the Ring would prove too great a temptation for him. Frodo willingly decides to carry the Ring to Rivendell, thus sending him out from the comforts of the Shire into the wide expanse of Middle-earth.
The Fellowship of the Ring Was Destined to Fail
Frodo is immediately faced with his first test as a hero when he has to contend with the Nazgûls chasing him. He also has the persistent test of refusing the temptation of the Ring and is even told explicitly to not put it on. Frodo is able to escape the Nazgûls, but he fails in not putting on the Ring. At the Council of Elrond, Frodo meets his travel companions. He has now gone through tests, met his allies and has faced his enemies with more to come.
However, there is the issue of who can Frodo trust among his allies. It is the Ring's influence over Boromir that contributes to Frodo breaking from the Fellowship and being forced to face his journey to Mordor alone. The longer that Bormoir travels with Frodo, the more he desires the Ring to the point he is tempted into trying to take it from Frodo. At that moment, the Ring essentially forces Frodo to break away from the group and also plants the seeds of paranoia within the Hobbit.
Frodo Fails at Being the Hero
With the arrival of Gollum, Frodo must finally face the ordeal of traversing through Mordor to reach Mount Doom, which is the next step in his hero's journey. The Ring tries harder to exert its influence over Frodo, attempting to lead him into Minas Morgul toward the Witch-king and exhausting him the closer they get to Mount Doom to prevent him from reaching his goal. Sam keeps Frodo from fully succumbing to the Ring's will. However, the Ring and Gollum make the paranoia grow in Frodo, resulting in him sending Sam away. The Ring becomes a more active interference in Frodo's journey the further into Mordor he goes.
This paranoia nearly results in Frodo's downfall. Without Sam to protect him, Frodo blindly follows Gollum into Shelob's lair and is nearly killed. Frodo is only able to overcome this ordeal because Sam returns for him. The Ring fails in influencing Frodo to reject the protection of his friend, so the only means it has left is to continue to exhaust him and hopefully expose him to Sauron. When it finally comes down to the final leg of Frodo's journey, or his "resurrection" as Cambell puts it, Frodo fails. The final climax of The Return of the King is meant to be Frodo tossing the Ring into the fires of Mount Doom, but instead, the Ring finally imposes its influence on Frodo to protect itself, and he puts on the Ring. Despite all the warnings from Galadriel, Elrond and Gandalf along with witnessing firsthand what the Ring does to someone like Gollum, not even a simple Hobbit like Frodo could resist the Ring's influence.
Frodo was allowed to bear the Ring because of who he was, a Hobbit with nothing to gain from the Ring and who had some natural resistance to it. Yet in the end, he failed to destroy it. Instead, it was luck that resulted in Gollum stealing the Ring and falling back into the fires. Frodo's personal hero's journey was always destined to fail because the Ring was a temptation itself. As Frodo came closer to Mount Doom, in an effort of self-preservation, the Ring worked to undermine his hero's journey. It didn't matter how virtuous or heroic Frodo had become over the course of his Lord of the Rings travels, in the end, he was no match for the power of the Ring.