challenge
Naujos pareigos jam tapo rimtu iššūkiu, bet jis su juo susidorojo.
The new position became a serious challenge for him, but he coped with it.
Memory lets a word go along a curve. Spaced repetition puts the next review just before the word slips, so every repeat buys more time than the one before it.
Seven cases, no shared vocabulary and a stress mark nobody writes down. What is genuinely hard about Lithuanian for an English speaker, what is easier than advertised, and the order that works.
Verba sends a short dictation every morning and brings the word back exactly when it starts to fade.