Sara, that's a great question that I often struggle with when I'm designing. In creating this example, I opted not to include directions in different spots for different reasons.
In a couple places, I omitted directions because I had hoped that the design was intuitive - like, click the numbers to reveal the timeline or clicking each major figure's portrait to learn more. In those instances, I certainly could have (and perhaps should have?) added directions, but omitted for the aesthetics.
With the underlined names in the timeline, I omitted directions to click on the names because it wasn't essential to the step - certainly, I included the capability if someone experiencing it wanted an immediate biography, but I consider it auxiliary to the timeline itself (kinda like having a term hyperlinked to open its definition in a glossary - not essential, but a nice touch if it's needed.)
Certainly a great discussion topic.