Depicts grain (來) being rolled between the fingers in the left hand (左). Based on the original meaning "rub between fingers", now written as 搓. The meaning later shifted to "uneven" and "error".
差 and 左 don't sound similar in modern Mandarin due to historical phonetic changes. They were more similar in older Chinese.差 /*tsʰraj/, /*[tsʰ]raj/, /*[tsʰ](ˤ)raj/, /*tsʰraj/, /*[tsʰ]ˤaj/ 左 /*tsˤa[j]ʔ/, /*tsˤa[j]ʔ/, /*tsˤarʔ-s/