I think it's all about appreciation like you say, and what is appreciation. For me it's being an optimist because you choose to realize and treasure what you have and be thankful for it as opposed to focus on the things you don't have. 
My favorite quote is:  "We tend to forget that happiness doesn't come as a result of getting something we don't have, but rather of recognizing and appreciating what we do have." - Fredrik Koeing. I think it's great to have this habit like you suggest to atleast once every day ask what am I thankful for. Today I am thankful for just having started my holiday and that I can spend it with my wonderful wife ;)