a good assistant uses their skills to help the master focus on their skills

Question

I have seen this sentence in lots of websites and I'm really confusing about it:

a good assistant uses their skills to help the master focus on their skills

When A good assistant is singular, why it says their skills while their is plural. It's the same for master and their skills.

I'm wondering if it is a grammatical mistake which lots of people are doing their websites, or a type of exception which I'm not aware about it.

I'm now confused about the real meaning of this sentence.

Answer 1

Good question (+1) as it confuses many.

When the first noun is epicene, the following noun can take pronoun 'they'. It's a common practice.

For example:

A client comes to you and does not find your website user-friendly, they will never come back.

A client serves as an epicene.

Useful reading about singular they will also help you understand it better.