Basically the issue was that the person playing as Sauron's forces only had to entrench around Mt. Doom instead of wasting time going out and trying to locate the ring-bearer. The only way for the ring-bearer team to win, was to get to Mt. Doom, so Sauron knew where he was eventually going to be. It didn't matter were he happened to be at any one time.
http://boardgamegeek.com/boardgame/2228/war-of-the-ring
Basically the issue was that the person playing as Sauron's forces only had to entrench around Mt. Doom instead of wasting time going out and trying to locate the ring-bearer. The only way for the ring-bearer team to win, was to get to Mt. Doom, so Sauron knew where he was eventually going to be. It didn't matter were he happened to be at any one time.