We learn something not only when we connect it to prior knowledge and try to understand its broader implications (elaboration),

but also when we try to retrieve it at different times (spacing)

in different contexts (variation),

ideally with the help of chance (contextual interference)

and with a deliberate effort (retrieval).

The slip-box not only provides us with the opportunity to learn in this proven way, it forces us to do exactly what is recommended just by using it. We have to elaborate on what we read just to be able to write it down and translate it into different contexts. We retrieve information from the slip-box whenever we try to connect new notes with old notes. Just by doing this, we mix up contexts, shuffle notes and retrieve the information in irregular intervals. And along the way, we further elaborate on the information, which we always retrieve deliberately.