When faced with a decision (e.g., like what to do on a week night), our final decisions are based less on what options are available, and more on what options we consider.
The options that come to mind most easily are the options that form our consideration set, and then we choose from that set. The problem is that often our consideration sets are limited—we are tired, we are in a “week night” state of mind, or we have only seen advertisements for certain things lately.
To increase your happiness, keep a running “to do sometime” list of things you want to do. That way when your consideration set fails to include a highly desirable option, you can simply turn to your this list for an idea.
For the original research on this topic, see: http://www.haas.berkeley.edu/Courses/Spring2000/BA269D/Negungadi90.pdf