So that you can eat healthy all the time, a positive and healthy lifestyle is an important factor throughout everyday life. If their work, their partnership, or something else gives them insecurity or even makes them unhappy and they cannot find enough balance in other areas of life, then your body will come up with a need for possibly unhealthy foods, thwarting your best eating plans.
The result shouldn't even be there, that they will not succeed in losing weight or changing their diet - they would just lose a lot more energy than necessary, to fight her lust, and develop a need at the same time, to compensate for their reluctance in any way - for example through the process of "losing weight", which is very respected in society, which can certainly provide some satisfaction.
In any case, one can assume that it will, that a large part of the dissatisfaction, that you feel during a diet (even if you eat enough low-calorie foods, for example) due to this feeling of inadequacy.
A holistic change in lifestyle towards one's own satisfaction and peace with oneself is therefore an important first step for a permanent change in diet - otherwise one will use far too much time, to think about, what you are not allowed to eat right now - and thus be exposed to a feeling of great dissatisfaction.