When I started playing magic four or so years ago, one of the first rules you learn is how the game ends. Besides decking and poison, your life total must remain above zero. During this time I would defend that limit relentlessly.
It seemed such an obvious position to take. Why would you help your opponent by paying life for fetch lands? I would find myself shying away from cards like Sign in Blood and Dark Confidant. I felt that it was inherent card disadvantage to hurt yourself, because your opponents use cards to bring your life total lower. An adequate justification for my position at the time, or so I thought.
What I didn't realize then would dawn on me at the first visit to my local card shop. This was during Scars of Mirrodin Standard. I was standing by the display case with some of my friends, and I saw the card Arid Mesa. I said to my friends "Hey, why are these lands in mono-color decks? Isn't it strictly worse to run this instead of a basic land? All it does is hurt you."
I'll never forget what one of them replied with. They are the words spoken that heralded my rebirth as a magic player.
"They thin your deck. You draw less land."
At that moment, I caught my first glimpse of what it was really like to battle your opponent in Magic. It is so much more than a struggle over life totals. There's a struggle for advantage and disadvantage, pressure and defense, timing and planning, cards in hand, and creatures on the battlefield. Your opponents DO spend cards to lower your life total; but only inderectly so. They spend cards to increase their overall advantage, which they then use to lower your life total.
I gained justification for this way of thinking when New Phyrexia showcased Phyrexian Mana in an environment of Infect. There were some matches where your life total meant literally nothing.
Which brings me to my conclusion, kiddies. Don't be afraid to pay some life. The only point of life that matters is the last one. Sometimes you need to lose a finger to gain the upper hand.