Those are damn powerful words. And they are very true. You can be grateful if it works for you. But if you're not, it isn't a moral or ethical failing. You aren't a bad person for being unhappy with how your life is unfolding. Bad things happen, and denying their existence doesn't help anyone at all.
The most natural things to be grateful for are the good things. So if you can, today focus on those things you CAN be grateful for. It's not raining or snowing, the temperature is warmer, my garlic is up, and I got out of bed today. I can be grateful for those.