This "living deliberately" is the key to what Nick is seeking through the restorative and recuperative powers of nature. He has seen first-hand the horrors of war (World War I), was seriously injured himself and suffered a mental breakdown. He is searching for some way to put the horrors of these experiences behind him and restore himself to a healthy emotional life. To do so, he feels that he must isolate himself from the rest of humanity until he regains his own sense of sanity and humanity.
Interestingly, trout fishing plays an important role for many of Hemingway's male characters. For example, in The Sun Also Rises, the main character, Jake Barnes, who, like Nick, was seriously wounded in the war, goes with his best friend to the Spanish Mountains for some trout fishing, especially when he is about to lose control of his life. Ultimately, the traditional Christian symbols of fishing and water become symbolic of Nick's being rebaptized into life. However, even though two prominent Western world symbols have been mentioned thus far, this is not a story whose meaning relies on symbols. Instead, it is a realistic account of a fishing trip during which Nick regains control of his life.
Two major, over-arching themes can be seen in each part: recovery in Part I and recollection in Part II.
