What challenges does Jack Smith face?

1. There are a lot of inexperienced soldiers
2. They have to make space in the jungle and clear trees out for camps
3. There are ambushes and tons of booby traps set by the Vietcong
4. You witness our buddies getting killed.

How Does Jack Smith's attitude change?

At first he is very laizez faire and does't really care but then he realizes he is fihting for his life. He had to protect his freinds and his unit.