The Timeline is designed to allow users to view activity related to them, as well as interacting with other users. The Timeline Event feed displays a wide variety of events, depending on a user's settings.
The view you have of your own personal timeline feed contains the widest variety of events. Generally, it contains events related to you, your connections, and some major system events.
The view you have of someone else's timeline feed depends on two things:
Users have the ability to restrict viewing of their timeline by other users, through their Notification & Privacy options in their Profile Settings. If a user has chosen to restrict their timeline, you may need to request to connect to them, and wait for their approval before you will be able to view their feed.
Generally, you will only be able to see events that relate to the user you are viewing, and not any other users.