You are what you do (or "You do what you are")

Do you know the biggest factor in having a good day?

It's not what day of the week it is.  It's not the activities that occur throughout the day.

You.
You are the biggest factor.
You create the good day or you recognize the good day.  In either case it's (almost*) all about you.

The choices you make throughout the day, what you do, is who you really are.  The job you do and how you do it, the people you are with and how you interact with them, the things you chose to do are what make you you.

To have a good day people have to look at themselves and see what they are doing to make it good.  They have to find ways to overlook or overcome or avoid the things that prevent it from being good.

Having or making or recognizing a good day is all about the individual.  It's all about you.  It's about what you are doing.

If you want a good day, do good day things.
You are a good day.