Everybody has limits. Nobody has 100% self-discipline. Except maybe a few unique individuals like David Goggins.

If you think you can do anything, you just haven't tried something hard enough. Or, you're super fit, probably running ultra-marathons or squatting 300lbs+. No junk food, no video games or TV, no breaks (even during commutes). And you routinely spray yourself with pepper spray, expose yourself to negative temperatures, withstand electric shocks, just to prove to everyone how strong you are. Because that kind of stuff makes you proud, makes you famous, and helps you make money (if selfish) or raise money for charity (if selfless).

Understanding your limits is essential to even reach them. Because if you push yourself too hard, you'll burnout - you'll cave into binge eating or injure yourself with bad form or develop weird symptoms from stress. You have to pace yourself. Even top-tier PhD students, athletes, billionaires understand.

In fact, if you come in with the mindset "I will try as hard as I can", your brain will make "as hard as I can" less. If you're afraid of failing yourself, you'll never really try. If you have any cravings for junk food or rest or anything, it's a part of you that wants those things. And the more you delay them, the louder that part of you will get.

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I speak from experience: I had the same "I have no limits" mentality. It led to burnout and crippled my athletic performance. It still does now, because I still kind of have that mentality - I'm super stubborn, and I hate wasting effort or committing to something and failing.

I always did my morning workout, but spent hours waking up. I always ran as much or more than planned, but I ran slower and slower. I ate vegetables and lean protein, but I ate more and more until my appetite was massive. Most notably, I lost my strong temperament, and got very emotional and anxious.

Once I started setting more reasonable distances and sticking to them, waking up became easier. Once I started eating higher calorie foods, my appetite went down. My emotional regulation is back. Even now, every time I have a fixed time I have to run (because e.g. I have an appointment after), I always run faster.

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In order to truly reach your limits, you need a plan to handle your weaknesses. You need to set goals - e.g. "I will run 5 miles today". And then don't run 6, even if you feel like it, or at least don't run 6 too often. Otherwise your brain will start pacing you for 6 instead of 5. If you're running is too easy, increase the distance slowly, like 10% per week. Otherwise you might injure yourself.

Same exact with eating. If you suddenly eat 500 calories one day, you might find that you're not really hungry. But if you keep eating 500 calories after a few days you'll get hungrier and hungrier, and that hunger takes a few days to go away. Calculate your TDEE and set a reasonable deficit, and if you're not losing weight after a couple weeks, then eat less. If you look at people who've successfully lost weight vs. fad dieters, the former practically always emphasize sustainable changes and self-love, and the latter are always beating themselves up and doing extreme stuff.

And most helpful to me, follow the 5-minute rule. If you really don't want to do something you planned, do it for 5 minutes. You have to work out every day, study every day, etc. no matter how bad you feel. But only for 5 minutes, and if you still feel awful that's enough. If it doesn't actually help you accomplish anything (because you only did it for 5 minutes), it will at least make you feel better, because you at least tried. And I can guarantee that most of the time, you'll keep going after 5 minutes.