And when it retires, you will give up on achieving your goal.
В этом тексте: The challenge is it will always require strong willpower to achieve any bigger goal. Willpower is like your muscles. It becomes tired, the more you exert it. And when it retires, you will give up on achieving your goal
And when it give out, you will give up on achieving your goal.
Edited* * *
The challenge lies in the fact that it will always strong willpower to achieve any bigger goal. Willpower is like a muscle; the more you exert it, the more tired it becomes. And when it give out totally, you will also give up on your goals.
Chel, don't feel bad if you have trouble understanding this - it's not very good English. The grammar is very sloppy and even I don't know what they mean by RETIRES. I guess they mean GIVES OUT. Muscles give out when they're too tired to work anymore. I've never heard of muscles retiring. I don't recommend that you use this text to learn English.
Спасибо за помощь!
Не, я не учу по этому язык, я просто переводил нужную мне статью и тут такое.