English is not the hardest language to learn, but still there are students who find many topics not quite easy to understand. If you ask a Ukrainian learner about the most complicated grammar topic to study in English, I believe it would probably be the articles.
Firstly, there is no such a notion as an article in the Ukrainian language, that’s the main reason why so many learners find it challenging to remember and use it correctly. People of different ages and levels of English can spend years using English as their second language, use a wide range of vocabulary, read Shakespeare’s poetry in original and still confuse articles “a” with “the” or omit them completely. We’d rather say what we want and people will understand us, so why bother remembering the articles?
The other reason is the simplicity of the topic, which with time can cause difficulties. At first, the explanation may seem simple, which is “a” for indefinite nouns, and “the” for definite ones, students talk and start easily. The problem starts showing up when they progress in learning. The information on articles usually gets bigger and more complicated on higher levels. There are a lot of exceptions, so it gradually gets harder for the learners to see the difference between the two.
To sum it up, articles is the most complicated topic for us, Ukrainians and in my opinion, maybe one of the most challenging to understand. Native speakers can use them naturally, but for those who don’t have such construction in their own language, it may be a problem.