1. The simple part: it's just a physics/thermo equation (i.e., calories in need to be less than calories out). Our bodies are not perpetual motion machines, if you consume less than you expend, you will lose weight.

2. The very complex part: everyone's second part of the equation (i.e., calories out) is very different. Some people's bodies burn calories very fast, some very slow, some have physical conditions that slow this part of the equation (i.e., thyroid, etc). Some can easily exercise to burn calories, some can't. It goes on and on. Again, everyone is very different.

The only way to lose weight is figure out how much your body burns, and then consume less. It's extremely hard for many people. But why is it controversial to say this? And yes, laziness is all around us to some extent.