A learning designer must take into account the changing state of the learner.

Here's a basic representation of a simple tool designed to help. All it does is map out a number of variables over a time period - in this case media richness, interactivity, and learning challenge - and colour code them. You can do this on a spreadsheet, a piece of paper or whatever. It might look really simple, but you'd be amazed how many learning designers I've seen use something like this and fundamentally change the quality of what they produce.