I am a young man who is inexperience in life but want to explore. I hear a lot of "you can do anything, if you just believe in yourself." But when I consider that there is a lot to learn, but our life span is short, I get scared. So I ask: Can one truly achieve anything by just believing in oneself?
When a statement by men contains a restriction, such as "just," warning flags should be raised. All it would take is one counterexample to disprove such a statement. Is it true that all you need to achieve a goal is belief in yourself? "I again saw under the sun that the race is not to the swift and the battle is not to the warriors, and neither is bread to the wise nor wealth to the discerning nor favor to men of ability; for time and chance overtake them all" (Ecclesiastes 9:11). The best warrior doesn't win every battle. The wisest man doesn't always make the correct choices. The best runner doesn't win every race. Is their lack of success due to a lack of belief in their abilities? No, God said that sometimes people fail simply because of bad timing or bad luck. In other words, there are always circumstances outside of your control that will change whether you succeed or fail.
Now it is true that if you don't have some confidence in yourself, you won't even try. If you don't try you won't accomplish anything. "The way of the lazy is as a hedge of thorns, but the path of the upright is a highway" (Proverbs 15:19). Therefore, believing in yourself makes it easier to accomplish something, but it isn't a guarantee of success.
You are correct that life is short and you won't have time to do everything that you would like to accomplish. But doing nothing will get you even less done. You can't allow yourself to get locked up in fear. Rather, realizing that life is short means we have to use what little time we have with energy. "Whatever your hand finds to do, do it with all your might; for there is no activity or planning or knowledge or wisdom in Sheol where you are going" (Proverbs 9:10).
Have fun. Enjoy your work. But don't forget what is truly important in life. "Rejoice, young man, during your childhood, and let your heart be pleasant during the days of young manhood. And follow the impulses of your heart and the desires of your eyes. Yet know that God will bring you to judgment for all these things. So, remove grief and anger from your heart and put away pain from your body, because childhood and the prime of life are fleeting" (Ecclesiastes 11:9-10).