11 When the sentence for a crime is not quickly carried out, people’s hearts are filled with schemes to do wrong.

Read Ecclesiastes 8:11 Using Other Translations

Because sentence against an evil work is not executed speedily, therefore the heart of the sons of men is fully set in them to do evil.
Because the sentence against an evil deed is not executed speedily, the heart of the children of man is fully set to do evil.
When a crime is not punished quickly, people feel it is safe to do wrong.