As someone with anxiety and depression, I can attest to the truth of this quote. It doesn't matter what talents, abilities, or support system you have in your life. If you don't know where you fit in or why you are on this earth, you will live in existential dread. I don't pretend to have the answers, but I will say this: even Superman went through it. He may be a godlike alien for whom life should be easy, but that isn't the case. It took soul searching, meditation and doing his best to help others in order to overcome it, to find that his love of people (and Lois in particular) was his reason for existing. I think that is a great place to start.
In contrast, Zod was genetically engineered to be a Protector of Krypton and he was a slave to that pre-determined role. He never doubted his reason for existing. But once Kal had banished his Kryptonian crew to the Phantom Zone, Zod's purpose ( his "soul") was gone and resulted in his trying to take Kal's from him.
Tl;dr if you're struggling with finding out who you are and why you're here, know that you are not alone. I'm on that path of discovery as well and though it's not easy there is always Hope. As Jonathan Kent said "I believe that you were sent here for a reason, and even if it takes you the rest of your life, you owe it to yourself to find out what that reason is."
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