What does Biblo's early reaction to Gandalf and his later responses to the dwarves say about his character? Can you think of some other ordinary characters (fiction and real-life) who are pushed by circumstances to do heroic things?

At first Bilbo doesn't want to leave the comforts of the shire. He is happy being a Hobbit and Hobbits hate to travel let alone go into a dangerous adventure. Bilbo is a homebody like all Hobbits, content to stay in the safety and predictability of the shire. Consider a guy like Canada's Terry Fox who ran for cancer on one leg. Initially he held back on the idea, comfortable in his home. He took the adventure anyway.

Anybody who embarks on an adventure has a calling. This is known as the Hero's calling in mythological terms. They usually refuse the calling at first and then agree to it.

Ps. Terry Fox ran across most of Canada through brutal weather finally succumbing to his disease.

At least as far as the film goes, Scottish hero, William Wallace, returns to his home village only wanting to wed his love and start a family, but the dreadful circumstances, as well as his education, compel him, and propel him, from vengeful clan member to heroic martyr.