Why is it so difficult to write the history of contemporary science?
Endeavour. 1999;23(1):1-2 
Thinking and Reasoning: Why is Logic So Difficult?
Fundamentals of Human–Computer Interaction. 1985;57-63
WHY IS IT SO DIFFICULT TO REFORM SOME ASIAN BUREAUCRACIES? BUILDING THEORY FROM CAMBODIAN EVIDENCE
Public Administration and Development. 2013;33(4):275-285
Why high-profile journals have more retractions
Nature. 2014;
Drug Comparisons: Why are They so Difficult?
Cephalalgia. 2000;20(2_suppl):25-32
Why changing the U.S. health care system is so difficult
Social Science & Medicine. 1993;36(3):iii-vi
Why Is It so Difficult to Reform Dismissal Protection?
Swiss Political Science Review. 2013;19(4):570-575
Research into practice: why is it so difficult to get a GRIP? A discussion paper
The Lancet. 2013;382:S19
Why is it so difficult to die?
Nurse Education Today. 2001;21(8):679-680
Why are trials in palliative care so difficult?
Palliative Medicine. 2000;14(5):435-435