Questions & Answers about Svaki čovjek ima svoj izbor.
Why do we use svoj here instead of njegov or njihov?
The word svoj is a reflexive possessive pronoun, meaning it always refers back to the subject of the sentence. Because the subject is Svaki čovjek (Every person), we use svoj to express that the choice belongs to that person. If we used njegov (his), it would mean every person has some other specific man's choice.
Why is the form just svoj and not svojeg or svoga? Isn't it the object of the sentence?
You are right that it is the object, which means it needs the accusative case. However, izbor (choice) is a masculine inanimate noun, meaning it is not a living being. For masculine inanimate nouns, the accusative case looks exactly the same as the nominative dictionary form. Therefore, svoj does not change its ending here.
The English translation says 'their own', but isn't čovjek singular?
Could Svaki čovjek also just translate to 'Every man'?
Yes, it could. The word čovjek literally means 'man' or 'human'. In this context, it represents humans in general, which is why 'Every person' is usually the most natural English translation.