Which friends appear in the left column of my facebook profile?

We have always wondered as to which friends appear in the left column of our facebook profile. Here is what facebook, itself says:

The left column of your profile may display different types of people in your life:

We highlight your friend list.

By default, a changing selection of friends always appears under the "Friends" heading in the left column of your profile. The selection includes many friends who you publicly interact with the most. Examples of public interactions include Wall posts, comments and mutually attended events — Facebook will never show friends based on whose profiles you choose to view or who you interact with over messages and chat.

You can choose custom friends to highlight.

In addition to your general list of friends, you can choose to feature specific friends (e.g., best friends, roommates or coworkers) or groups to which you belong.

Your family and relationship partner appear here, too.

If you choose to add family members or a relationship to your profile, those people will also be featured in the left column. 

So now we know! :)