Knowledge
Knowledge is the essential source of life after water.
Water and food help your body stay strong and in shape and helps you survive on Earth. But knowledge help you under how to survive, what you should do to survive, what tools you need to survive, what's healthy and not healthy amongst plants and goods you find on Earth, how to take care and produce what will help you survive.
On the other hand, it helps you understand well how to control your life and how to deal with different situations you face, either in teryof your relationship with others, or in terms of natural disasters and unwillingly surprising events happening that you need to take action about, either to survive or to control your mindset and have steady and happy life as possible.
Lots of people around the world are suffering from depression, anxiety and lots of psychological reactions they couldn't control and science couldn't find real cute for it. Because simply, it is something psychological that the person him/her self needs to find the appropriate way to control their feelings and the way they are thinking. And that's not going to be happened unless the person gets the knowledge about what makes their feelings and thinking unstable, and convinced him/her self that they can go out of the closed circle they put themselves in. And most importantly by understanding that the past is gone and can't be back. And they should focus on the present what they can do, what they're able to do, and what they need to do, do that they can build their future.
Knowledge is required in all aspects and fields of life. Without knowledge you will never know how to be good to others, how to react the proper way to rude or bad people, how to protect yourself and your beloved ones, how to care PROPERLY for people around you whether the closest ones to you or to the entire world. Without knowledge you would never be able to use any tools or to manage anything in your life...... Your life is going to be miserable!