For me, it's not winning or losing. First off.... It's for the sense of adventure and the feeling that it's you against the world. Seccond, it's about attempting to top my tonnage reccord with every career. I always use SHIII Commander to keep track of kills and total tonnage. When I die, I go back to 1939 and start a new career with the goal of lasting longer and beating whatever my reccord tonnage is (I was about to pop in to tell Balz that I topped his first GWX 2.0 patrol with mine but when I logged in, he had just posted his "Balz gets One Million Tons in One Mission" thread. Oh well... gives me something new to strive for.)
My ultimate personal reccord for me to beat so far is 216850 tons and I'm nearing that in my current career so I think I'm going to set a new reccord for myself.