The Need for Calculation

Sun Tzu teaches that you must calculate the balance of forces before a battle. Strategy usually looks for ways to winning by avoiding opposition, but, when meeting an opponent is necessary, you can know if you will win or lose given meeting beforehand if you compare the five key elements that determine the strength of a position. You can thereby avoid battles that are certain losers. Politicans are particularly bad about picking battles that are certain losers. You can pick your own example from the news, but here is a recent example from Barrack Obama:
Democratic presidential candidate Barack Obama says he doesn't wear an American flag lapel pin because it has become a substitute for "true patriotism" since the Sept. 11, 2001, terrorist attacks.
Hillary's positioning has forced Obama and Edwards to go the left, but I cannot fathom any calculation on Obama's part that came to the conclusion that a stand against flag pins wins more votes than it costs. All you can think is that Obama picked this particular battleground without any thought at all. No wonder Hillary's lead is up to 33 points. She doesn't make a move without calculating its potential in votes. She doesn't even have to act to take advantage of these mistakes. Why is the simple element of calculation beyond the strategic abilityh of most politicians?