Depression, or acute sadness, can come because either we don't know our God given gifts or we aren't using our gifts for the glory of God.

Another reason for sadness in a believer, is thinking they earn their holiness when it is only by grace; it is a gift from God.

Trusting God during trials causes our faith and trust in God to grow.

Count your blessings.

Sometimes we forget what we should we remember, and remember what we should forget.

Sometimes we forget what we should we remember, (like our blessings & how blessed we are) and remember what we should forget (like past trials, failures, forgiven sins).