Some aspects of English that are commonly found difficult by learners include:

1. Pronunciation: English has many irregularities in pronunciation, making it challenging for non-native speakers to know how to correctly pronounce words.

2. Grammar: English grammar rules can be complex and have many exceptions, making it difficult for learners to master.

3. Vocabulary: English has a large vocabulary with many words that have similar meanings, making it challenging to choose the right word in context.

4. Idioms and phrasal verbs: English is full of idiomatic expressions and phrasal verbs that can be confusing for non-native speakers to understand and use correctly.

5. Spelling: English spelling rules can be inconsistent and difficult to remember, leading to frequent spelling errors.

6. Colloquialisms and slang: English has many informal expressions and slang terms that can be difficult for non-native speakers to understand and use appropriately.

Overall, mastering English requires a lot of practice and exposure to the language in various contexts.