If you cook and you like garlic you'll know that you need to add more to 'notice' it. The smell of fresh bread wafting through a supermarket which is so delicious on first entry soon gets 'forgotten'. The speed of a microwave, the ease of e-mail on the go from a phone, a decent salary from a good firm. These too become the new norm.
The point? It doesn't take long for us to forget how lucky we are.
Take a moment. And a pencil and paper. Write a list of things for which to be grateful. Do not dwell on changes you would like nor imperfections. Simply-for once-notice what is pretty damn good. For most of us, in this corner of the world, it's a great list.
Keep it on your desk and re-write every week from memory. You'll feel better. You'll feel happier. You'll have gratitude.