Across a set of 45 catalogued ESL error patterns, the largest single category is article misuse. It ties with preposition errors at six patterns each, and it dominates the highest-frequency ranks.
The reason is structural rather than careless. Many first languages have no article system at all, so there is nothing to transfer. "She is teacher" is not a slip; it is a correct sentence in the grammar the speaker already has.
The three patterns worth learning first, because they cover most cases:
- Singular countable nouns need an article. "I bought car yesterday" becomes "I bought a car yesterday."
- Unique or already-mentioned things take "the". "Sun is bright today" becomes "The sun is bright today."
- Abstract nouns used generally take no article. "The honesty is best policy" becomes "Honesty is the best policy."
That third rule is the one that trips people who have over-corrected from the first two.
Grammar tools that flag these patterns are at belikenative.com.