因
yīn · HSK 6
because
📦 大 (big) trapped inside 囗 (box) — every big thing has a cause
The structure locks 大 (big) inside 囗 (enclosure). Bonus: yīn sounds like English IN — the reason is right there IN the box.
因 — enclosure 囗 + big 大
因 originally pictured a person (大) lying on a mat or cushion, shown by the surrounding box (囗). The original sense was 'mat' or 'to rely on,' which extended to 'cause,' 'reason,' and 'because of.' The 'mat' meaning was later written with 茵.