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 Boolean Complexity Theory so Difficult?
Boolean Function Complexity. 1992;84-94
Why high-profile journals have more retractions
Nature. 2014;
WHY IS IT SO DIFFICULT TO REFORM SOME ASIAN BUREAUCRACIES? BUILDING THEORY FROM CAMBODIAN EVIDENCE
Public Administration and Development. 2013;33(4):275-285
Commercializing technology: why is it so difficult to be disciplined?
Business Horizons. 2004;47(1):65-71
Why is it so difficult to die?
Nurse Education Today. 2001;21(8):679-680
Why is Margaret Thatcher so difficult to interview?
Ethology and Sociobiology. 1989;10(5):399-400
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 Teach and To Learn ?
Group Analysis. 1975;8(1):46-52