I recently answered this question on Quora and again thought about expanding on it a little and sharing it here.

(depression can have many causes, I'll write more about depression in future posts)

I think looking at our life and examining it could help us find a source of that spells of depression.

There is something we're NOT doing (suppressing something within us) that our heart wants us to do. We usually stop ourselves from doing stuff we want doing out of fear:

• fear of change (even positive change)
• fear of failure
• fear of discomfort
• fear of what other people will say

An Example...

So let's say you want to be a photographer, you want to travel, you want to be a musician. But you're looking around and find reasons (read excuses) not to do that. It won't pay you enough money, you're too old, your spouse won't accept it, people will not understand...

You're rational, logical and you decide that what your heart is "telling" you to do is just a silly idea. So you put those feelings, that urge of doing what you want doing aside. You bury it deep inside you, deep down into unconscious...

and you feel good... for a while...

These feelings, emotions, urges, they want to be expressed. They are who you are and you can suppress them only for a period of time before they rise again. You may not know what they are right away, but look at them, when you feel these spells of depression, don't resist, don't hide. Bring them to awareness.

Depression often comes when a person can't express him/herself out of fear. No expression = depression.

Look at your life, what are you resisting?