One of the greatest elements of the show is that there is no rule for how the jury is supposed to vote. You can't objectively compare the finalists, because there's no set yardstick with which to measure them.
The net result is that we've had bizarre combinations of reasons throughout the years: who screwed over the most people, who didn't screw over the most people, who worked the most in camp, who had the most need back home, who had the biggest sob story, who was the best at physically surviving, who was the best leader, who was the best flipper, who had the least odious personality, etc. Shoot, the guy that won the China season won mostly by just repeating "strategy" at Final Tribal Council as his defense/rationale for everything.
Going into the season, you never know how the jury is going to base their decision, how much they've compared notes, and how bitter they're going to be. Your strategy has to account for all possibilities.