There are a few reasons why you might not see posts on this friends page:

• Sheldon might have no friends defined. If you are Sheldon, you can edit your LiveJournal friends so they show up here.
• Sheldon might have friends defined, but all of their friend's posts might be over two weeks old (according to the times on our servers), and thus wouldn't be displayed here.
• Sheldon might have friends defined that post only protected entries that you can't view, because they haven't defined you as a friend in return.