LISTEN, THIS IS THE TRUTH: "Though our feelings come and go, God's love for us does not," C.S. Lewis. LET GOD'S WORD - NOT YOUR FEELINGS - LEAD YOU: "Whoever trusts in his own mind is a fool, but he who walks in wisdom (God's Word) will be delivered," Proverbs 28:26.
It's really a metaphorical "tumor" that presses on your brain every day and makes sure that by the end of that day, you are once again reassured that you are the most worthless, hideous, disappointing monstrosity to ever walk the earth. That is what depression does to you. That is what depression is: a tumor of emotion.
It's often hard for others to understand mental illness but knowing that sometimes there is no clear reason to why some people have mental illness & others don't is a great star to understanding. Know that you can still be a good friend without fully understanding the whys of life.