Desirable Difficulties is a conceptual framework introduced by cognitive psychologist Robert Bjork (1994). It posits that instructional conditions which appear to slow down learning and increase errors during instruction often lead to superior long-term retention and transfer. Conversely, conditions that create rapid improvement during training often fail to support long-term durability.

Bjork (1994) argues that learners and educators often confuse "Performance" (immediate, observable ability) with "Learning" (permanent change in knowledge).

• Massed Practice (Cramming): Increases current performance (high Retrieval Strength) but creates little long-term learning (low Storage Strength).
• Desirable Difficulties: Decrease current performance (more struggle/errors) but trigger the deep processing required to increase Memory Stability (high Storage Strength) .

Not all difficulties are desirable. As noted in recent analyses of Cognitive Load Theory, a difficulty is only desirable if it is Germane (relevant to the task). Difficulties that arise from poor interface design or confusing instructions are Extraneous and merely hinder learning. Furthermore, difficulty must be calibrated; if the Intrinsic Load is too high for a novice, the difficulty becomes "undesirable" and leads to failure.

We intentionally engineer "Desirable" friction into the user experience while removing "Undesirable" friction.

• Desirable: We delay reviews until you are about to forget (Spacing) and mix topics (Interleaving) to force effortful retrieval.
• Undesirable: We remove complex menus and gamified clutter to ensure your working memory is free to tackle the language itself.

1. Bjork, R. A. (1994). Memory and metamemory considerations in the training of human beings. Metacognition: Knowing about knowing

2. McDaniel, M. A., & Butler, A. C. (2010). A useful perspective on student learning: The desirable difficulties framework. Psychology in the Schools, 48(1).