因 shows a person 大 stretched out inside an enclosure 囗 — originally a sleeping mat. What you lie on is what you depend on; dependence became grounds, and grounds became cause. The reason is what everything rests upon.
因为…所以… (because…therefore…) is the logic sandwich of Chinese — and unlike English, you say BOTH halves: 因为下雨，所以我没去 ('because it rained, therefore I didn't go'). Dropping the 所以 sounds abrupt to native ears. Buddhism deepened 因 into 因果 (karma — cause and fruit) and 因缘 (karmic affinity): the mat you lie on across lifetimes.
A person on the mat they rest on — the grounds, the CAUSE.
因果 'cause and fruit' is the standard Chinese word for karma — agriculture doing philosophy's job.