I have some troubles in distinguishing written characters 曰 yuē (to speak) and 日 rì (sun). Although they singularly look different on computers (maybe yuē look a bit wider, while rì is taller), I find it almost impossible to distinguish them when they appear in composite characters, or even alone in handwritten texts. Is there some difference I cannot catch that I should pay attention to? Do their writing differ in stroke order? Thanks!
As pointed out in some answers and comments, there are other sets of characters that look very similar. Among them: 口 kǒu (mouth) and 囗 wéi (enclosure); 人 rén (person) and 入 rù (to enter), 千 qiān (thousand) and 干 gān (stem), 已 yǐ (stop) and 己 jǐ (self)