What are the reasons to be depressed ?

There are numerous reasons to be depressed. One can even get depressed on the reasons which generally are not considered to be depressed. Like, I am a woman who has ,touchwood, everything fine going on in her life, but I still get depressed and sometimes reasons are apparent and sometimes, I myself do not understand why I am depressed. So, reasons for depression are not stated. One can be depressed for any known or unknown reason.