When you have a lot of Subjects, you can pin some of them to keep them displayed on the left column. By default, 100 subjects are displayed, sorted by name.

To do so, click on the subject you want displayed, then click on the star next to its name on the top of the screen.

Subjects can be unpinned to remove them from this list of always-with-you-subjects.

You can also prioritize / rearrange your pinned subjects simply by moving them into place with drag&drop.