When to consider a therapist for weight loss help?

In theory, losing weight is easy. Consume less calories than you burn, presto! Weight loss! Not rocket science. And yes, it's expected that kicking old habits to the curb is going to be mentally challenging. If it wasn't, losing weight would be a breeze for everyone who attempts to do so.

But at what point is it ok to admit one needs help, as opposed to feeling defeated and weak in the face of a challenge? And what exactly do therapists do to assist a person who chronically struggles with weight loss?