One of the biggest lessons I learned about getting in the best shape of your life (and keep it) is this: if someone is following a certain program and look great, that doesn't mean the same thing MUST work for you too. Obvious? In words, maybe. But how many of us have followed particular plans, misunderstanding that being dedicated and disciplined meant to be deprived and burned out on endless hours in the gym? To get in your best shape you gotta work hard, that's for sure. Dedication and discipline though are not only determined by how low your body fat get or how long you can go without seeing a once of carbs. Dedication, passion, discipline, motivation all those great words, have MEANING only if you are applying them in the right direction, which means toward a GOAL, realistic to YOU.
Not everyone want to be showing veins and striations (I like some but not in excess), not everyone desires to be below 10% bf for life and not everyone should think that if you don't deprive/beat yourself up day in day out, YOU are not working HARD enough and never will be lean as you want. It all depends by what your goal, start point/level of fitness and body type are.
Let's say the goal is to be lean enough to see great degrees of definition and you've been training few years already. Look at your body type. Are you short, muscular already and get "chubby" easily? Then yeah, more restriction on diet, more hrs on cardio. Are you short but skinny/fat? You might need to work more with weights then cardio, since you lacking the "raw material" aka muscle mass, and provide your body with enough nutrients from protein, CARBS and FAT. Are you tall, kinda muscular but hold fat as well? That means another regimen etc, training and diet wise.
There is nothing more frustrating than trying to stick to a plan, that give you little results and make you miserable. You have dedication, constancy, patience...and wonder why you don't see the results you want? Maybe It is not you, it's the plan. How do you know if it's the plan that is wrong or you are not working hard enough? If training is one of your priorities, you've been sticking to the plan several weeks already, you feel extremely tired after your sessions, intensity and drive are present in most of your workouts, you are diligent in your dietary choice, in short, you CARE about getting results and think you are sincerely giving your all, then... Time to REVISE the plan you are on!
Because muscles don't grow on a lettuce diet, fat doesn't melt if there is no "basement"(muscle) to support your metabolism... Just like if you have a tree and are waiting to see blossoming carrots from it. It just aint gonna happen!