愿

Bottom radical 心 in its full four-stroke form anchors 愿 as a mental/emotional state - the wish or vow that wells up from the heart. The heart radical groups 愿 with kindred mind-verbs like 想 (think), 念 (long for), 怀 (cherish), 恩 (gratitude) - all emotions surfacing from inside.

Top-left phonetic 原 supplies the sound - yuán shifted to yuàn through tone-change only. 原 itself depicts a spring 泉 emerging from a cliff 厂, the "source" of water. As phonetic in 愿, it gives the same vowel and consonant; same series produces 源 (yuán, source) and 愿 simply adds 心 to specify the heart-source: a heartfelt wish.