Being thankful is a choice. It's not a reaction or an impulse, it's something we choose to do.
Likewise, it's something we can choose not to do.
It may be easy to be thankful this week. It may be hard. It may be forced upon you at the dinner table as everyone has to say one thing they are thankful for (and you better not steal someone else's answer). But the reality is, no matter what, it's a choice. And we can always choose to be thankful.
Always give thanks to God the Father for everything, in the name of our Lord Jesus Christ. ~ Ephesians 5:20 (NCV)