A character written in the wrong stroke order still... looks like the character — which is exactly why these habits survive for years. Nobody corrects you, until your writing turns crooked, slow, and visibly "foreign". Here are the ten most common mistakes, each with the rule that fixes it.
Group 1 — Drawing instead of writing
1. Drawing 口 as one closed loop. 口 is three strokes: left vertical → horizontal-turn → bottom horizontal. Looping it in one motion is the single most common error — and every character containing 口 (吃, 喝, 名, 和…) inherits the damage.
2. Two-stroke 日 and 月. 日 has four strokes, 月 has four — the inner horizontals are separate strokes, not a convenient zigzag.
Correct: the 撇点 (left-falling + dot) is ONE bent stroke, then a left-falling, then the horizontal. Write 女 as three loose strokes and 好, 妈, 她 never balance.