why u talk like a pastor.No mortal has the ability to predict the future. In your case, although such minor surgeries are often successful, 99% most of the time, it is the 1% that most are frightened of, not just your housemate, but even yourself, of medical complications that may arise during surgery or later....thus the pessimism, of the unknown 1% chance...
Rather than to be pessimistic, to dwell upon that 1%, such would only make each other become even more fearful, in tears & hugs for comfort. It would serve no good to anyone, weakens the mind & eventually the body self healing systems.
As you are medically well, your housemate whom is in pain, seeks for comfort, assurance, guidance & critically hope from you - a close friend. And it is hope that gives birth to courage & optimism, to dwell instead on the 99% of chance.
Such is NOT false hope, as it is proven that most go thru such med assistance & survive well. Thus have courage & hope always, & to share it with rest of Humanity whom need such to go thru painful times....
walau