There is a book called "Bhagavad-Gita", also known sometimes as just "Gita". This is a very popular scripture for many people of India. This book is read and practiced in day-to-day life by many millions as the practical aspects of this book help in day-to-day life and suggest an easy adaptable way to conquer our inner darkness and attain the Supreme Being. The teachings of this book tell us that we should do our "karma" or action and duty without weighing the outcome of our efforts. It is our responsibility to perform action but it is not up to us to decide the results of our actions. Some words from Bhagavad-Gita where Lord Krishna says to his disciple Arjuna, "Perform all your actions, having abandoned attachment, and become indifferent to success and failure."
While it is true that the goal is what gives the motivation to persevere but if you are doing something to reach that goal and not really enjoying the journey, it is not worth it. In addition, sometimes if the end result is not what we had wished for, it can lead to frustration.
This book is available in book stores like Barnes & Noble, Amazon and most of the popular book stores. It has the original verses in Sanskrit (the language in which many Indian scriptures are written) and it then has the English explanation of the verses. Reading this will be an enlightenment and will help resolve many perplexing questions that come to our mind about life, deeds and actions. If you get a chance, I strongly suggest you read it at least once. You will enjoy reading this book as it is the form of questions and answers, answers to many questions that we are looking for in our journey through life. It will be an adventure that might transcend you into a whole new human being.