You do not need to work 70 hours a week. You would be more productive if you worked 40 hours a week. Beyond a certain point, more time spent is a net negative, because it hurts your ability to think clearly. Plus, even if it did make you more productive, the cost still wouldn't be worth it.

Thus, whatever is motivating you to work longer hours is mistaken. If it is your own belief, fix it. If it is the belief of the company you work at, either try to work with them to get more reasonable hours or try to find a new job.