How much sadness in your life is produced by your own thoughts? That's probably a difficult metric to determine however is an important concept to consider; In my humble opinion at least.
Some believe attitude is everything; I'm one who believes this simple but powerful phrase, however it is important, firstly, to understand where ones' attitude truly lies. Paying close attention to what pleases me, stimulates me emotionally and spiritually and to what sustains me is where that begins.
I've discovered, through life and the experiences within it, that I can observe my thoughts...And change them.
This is the key to maintaining the correct attitude.