JPDrills flashcards work on a levels system. Users start at level 1 with a limited pool of words. Answering correctly gives points towards reaching the next level. Upon reaching level 2 more words are added to the pool. Each new level adds more vocabulary to practice. But be careful! Answering incorrectly may decrease your level! In this way an equilibrium is reached where users continuously move forward, aren't overwhelmed with new and unknown words, and also gain positive affirmation by repeating and correctly answering words they do know.