Incorrect. There is no person a diet and exercise won't work for. You can not run a caloric deficit and gain weight. The laws of physics apply here.
According to the nasty, nasty fights I've had with people about this topic there are, apparently, some people whose bodies are actually perpetual motion machines and I'm various kinds of insensitive for even bringing-up physics as it relates to weight. >sigh<
Humans are not bomb calorimeters. The physics is undeniable and straightforward, but the biology is messy and hard.