He expressed a direct opinion.

He struggled to understand the object.

An intransitive verb represents the action or state of the subject, and does not require a direct object.

The subject is the most important part of a sentence.

He has difficulty expressing his emotions in words.

He showed his gratitude on his face.

He started to act immediately.

I couldn't understand his actions.

I'm worried about his health condition.

Your cooperation is needed for this project.