We are commanded to be thankful by the will of God.  One of the reasons is that thanksgiving is beneficial.  The benefits of thanksgiving follow.  

Thanksgiving yields contentment – you find that you don’t miss the things that you don’t have when you are truly grateful for all the things you do have.

Thanksgiving yields satisfaction – when you are thankful for what you have, you’re attitude about the things you have improves.  You appreciate those things much more.

Thanksgiving yields joy – when you consider how much you have to be thankful for you rejoice.  Thanksgiving puts a smile on your face.  A merry heart maketh a cheerful countenance [Prov 15:13].

Thanksgiving yields glory to God – 2 Cor 9:12-13 – when we are thankful, we acknowledge that all we have comes from him.

Thanksgiving yields strength against sin – Rom 1:21 – the main reason people get into the horrible sins of Rom 1:29-31 is that they are not thankful to God.  From this lack of gratitude comes the worship of nature, lies about God, vile affections, and a reprobate mind.

Conclusion: no matter what, be thankful.  Being thankful is one of the best things you can do for yourself.