For me, it is that simple. My point was that for my wife, there are a ton of other considerations she deals with. Sure, they're mainly in her head (though possibly other factors such as gut biome play a role), but large she has more details to factor in when she thinks about "will I be able to do this?". I on the other hand don't. For me, it's exactly as the author described, simple.
Yes, simple does not mean easy, but saying quitting smoking is simple to a smoker is not an honest assessment of their situation.
Most things in life are simple if you ignore reality and speak of life from a bubble.