I heard on a christian radio show one day that the main cause of anger was unfulfilled expectations. On the same station I also heard that depression is a result of quenching the Holy Spirit in some way. So if a person struggles with these they may have something that God is calling them to do that they haven’t realized yet. Probably due to feelings of inadequacy or even doubts that God wants to use them or bless them in a certain way.
Remember the best way to discover God’s will for you life is by asking what desires are in your heart? (Psalm 37:4). As you delight (or surrender) yourself in the Lord, He gives you whatever desires He wants you to have. Of course it’s human nature to doubt due to fear or unbelief, so many people end up living average lives with unfulfilled dreams.
Every christian has a God-sized dream that God wants them to accomplish that requires a closer walk with Him to carry out.