The presentation of the intellectual work of others as their own by students is believed to be common worldwide. Punishments and detection software have failed to solve the problem and have important limitations themselves. To go to the root of the problem, we applied an online questionnaire to 344 university students and their 13 teachers. Our objective was to compare their views on plagiarism and to test nine hypotheses about causation. We found that both students and teachers know what plagiarism is and that each group blames itself to some extent. Students blamed their own attitude but also mentioned their need to cope with an unnecessarily heavy workload imposed by teachers. Teachers blamed impunity and their own failure in providing meaningful and creative student work. Only 8% of the students admitted to plagiarising contents and admission was independent of need for higher scores, years in the university, sex, age, occupation, career or living in a small city where educational resources are more limited. We found that Spanish language literature has given more attention to the students' point of view than much of its English counterparts, and conclude that plagiarism can be prevented by an approach based mainly on a workload defined by teacher teams instead of isolated teachers; reduction of rote learning (associated with texts that are easy to copy and paste); assignment of individualised work that cannot be plagiarised (workshops, exhibitions, forums, portfolios, solving real cases, applying concepts to the student's personal experience); and accompanying students along the whole process of producing the written work.