Lieutenant Dan Taylor, Forrest's superior officer in Vietnam, has a lot to live up to. As Forrest tells us, "Somebody in his family had fought and died in every single American war." (Question: wouldn't it be more impressive if someone had fought and lived? Then again, we don't know much about war.)
It's not that Lt. Dan has a death wish or anything. In fact, he's a downright decent guy, and definitely someone you want on your side in a war. He's got two interests: protecting his men and winning the war in Vietnam, and he does everything he can to fulfill those two life goals, including swearing at Forrest to leave him to die when he loses his legs in a firefight.
Forrest, of course, carts off Lt. Dan anyway, and the experience nearly wrecks the guy. Instead of dying a hero, he ends up a wheelchair-bound cripple (in his view). In his own words: "I should have died out there with my men, but now, I'm nothing but a goddamn cripple, a legless freak!"
Gee, don't go easy on yourself or anything, buddy.
Destiny or Bust
Lt. Dan thought it was his destiny to die on the battlefield just like his ancestors. And check out that key word: destiny. If we've learned anything from Forrest Gump, it's that destiny doesn't come pre-installed, like some version of Windows you can't escape. We write our own destinies through our actions; it's not determined by who we are intrinsically. (Think back to Forrest's "stupid is as stupid does.")
So, when Lt. Dan says to Forrest, "Now, you listen to me. We all have a destiny. Nothing just happens. It's all part of a plan!" we're supposed to realize that he's wrong. Thinking that way turns Lt. Dan into a man who's convinced that his life doesn't matter since he's supposed to be dead. As you can imagine, the consequences are not good. He ends up sliding into brutal depression and alcoholism, and he adopts just about every abusive personality trait you can imagine.
But, Lt. Dan is a man of his word. You might say that he does what he says he will. So, when he cynically laughs that he'll join Forrest as first mate if Forrest ever does set up as a shrimping captain, he keeps his word: "I told you if you were ever a shrimp boat captain that I'd be your first mate. Well, here I am."
By doing that—by taking action for once rather than bemoaning his loss of destiny—Lt. Dan actually writes himself into a pretty sweet future as the part-owner of a multimillion-dollar shrimping company, a savvy early investor in Apple, the owner of a fancy pair of prosthetic legs, and, of course, a man with a hot fiancée.
Not bad for a guy who was supposed to die on a battlefield in Vietnam.