I have a "simple" problem where a piece of code somebody "wrote this morning" doesn't work. Its about thirty lines, has a pretty print harness and well define

I have a "simple" problem where a piece of code somebody "wrote this morning" doesn't work. Its about thirty lines, has a pretty print harness and well defined inputs and outputs - it normally takes a competent programmer about 15 minutes to solve in an interview setting (less than five outside). What absolutely shocked me when I first started using it is that it normally takes them 10 minutes for them to decide to insert any form of debugging code, and many try and not talk to me - despite introducing the problem as "a quick debugging task which we hope will show your willingness to talk problems over". Of course the man that took the biscuit was the one who, after I introduced the problem boldly stated "This is obviously a complex problem. If I had more time I would be able to solve it for you". No.