Work hard and succeed is the name of the game. I don't doubt that working diligently will have a better success rate than doing nothing, but I feel like we've taken the meaning of the phrase out of context. I'm not enabling those who refuse to make changes or sacrifices, what I'm saying is I think it's possible to work too hard. Everything says if you want something, no amount of work should seem like too much, but I disagree. You have to look at what your goal requires and what condition your resources are in. By resources, I mean your physical health, mental health, condition that you will be working in, and the things that can and will have a direct effect on the quality of your progress.
I'm going to use a hypothetical situation. Let's say you want to be a basketball player. More goes into being a great basketball player than naturally perceived. We think practice and you're good, but it's more to it that a lot of people take for granted. You don't have to be a giant, but your physical appearance and health definitely make a difference. If you have any medical conditions (such as asthma or a heart condition) that can be aggravated, you would need to be more mindful than a person who doesn't. Another factor is where will you practice? Do you have a hoop in your driveway, use an indoor gym, or do you have to walk to an outdoor court? I know you're probably thinking what difference does it make, but hear me out. If you're practicing at home, when you start to get burnt out, all you have to do is go in the house for a few and come back out. At an indoor gym, you just need to sit for a breather because you're already indoors. (Not to say anything can't happen). When you have to walk to an outdoor court, you don't really have any immediate protection per say from the elements.
Now, even though the goal is the same, you can kind of see where how hard you push yourself can possibly have an adverse effect on your progress. I live in FL, during the summer it's easily 100 º, keep that in mind. Best case scenario, you're totally healthy with a goal in your yard, practicing a total of 6 hours a day. It's pretty easy because you can just go outside in increments and get it done. Another scenario would be you have asthma and go to an indoor gym. You have to travel to the gym, but you have a ride so you go twice a day for 3 hours. While you're practicing, you have to take it easy a few times because of your asthma, but you have your meds and know when your body needs a break so you're fine. There's more to be mindful of, but you've adjusted your practice so you don't over stress your body. Here's the worst case scenario, and I feel a majority of people fit into this category. You have to walk to an outdoor court to practice. You're healthy, but you don't get as much rest as you should. Since you have to walk and want to practice as much as you can, you opt for a 6 hour block from 2 - 8 PM so you don't get home too late. Immediately it seems like a sacrifice you have to make if you want to reach your goal. Even though your mind is up for it, your body may not be able to keep up. Sleep deprived and experiencing heat exhaustion, you collapse. Maybe not day 1, could happen in week 3, if you're lucky it won't happen at all or you may just feel like you'll pass out and don't.
I love to see people who are ambitious about their goals. It's so inspiring to see people progress with no odds in their favor, but you have to remember that your mind and body don't have the same limit. I'll tell you all the time, reach for the stars and think big, but you have to be considerate of your body. You can tell yourself over and over in your mind that fire isn't hot, but if you set a body part on fire it's going to burn, no matter what you think. Keep striving for your goals, but don't overexert yourself because of the next person. Listen to your body, you know it better than anyone in existence. Praise yourself for the progress you have made instead of overworking and burning yourself out because of what you feel you haven't. Being busy and making progress are not the same. You'll get a better quality of work if you take time to reset occasionally when you need it, it doesn't even have to be a whole day off. Just make sure you take care of you too, you are just as important as your goals.