There were two poor and homeless brothers, the elder one was of 9 years and the younger one was of 6 years. They somehow managed to have alms. However, one day the elder one got sick, now the younger brother couldn't find enough food to eat and money for treatment for his elder brother.
He hopelessly sat down under a tree and saw some workers digging a hole and were paid for the labor. He decided to do the same. But why? why, why, why? Why did he need to do this, he was just a 6 year old kid, so why would he do such a tough job?
Because he wanted his brother to be healthy again, he wanted money to survive. Even though he was just a 6 year old weak kid, he did that and made his brother to get treatment.
The difference between that kid and us is that we forget to ask question, WHY? We don't feel the importance of it as he felt. If you are drowning in a river, you will try your best to survive, it's because you want to live like anything else, you will give your best, you won't wait for anyone to motivate you, you will try harder with each passing second till you can, Won't you?
Motivation lasts longer when it comes from inside. How much someone motivates you, how many books you read, can't motivate you till the end. Outside motivation is used to enlighten the hidden fire inside you, it doesn't put the fire, it just helps to find out it.
So, the importance is not of motivation you need, it's of the fire you should have for your goal.