[原创]What is your biggest problem?

In interview, employer always ask you what is/are your biggest problem(s) in future position. How will you give one professional answer, which satify your future employer?

Some days ago, I applied one position of Project Mgr # one battery manufacturer. (BTW, high salary :-) 15K/month) One of their Sr Manager asked me what is the biggest problem in future position if he hire me.

I answered it is the professional knowledge on battery. I must deep know all manufacturing processes within some weeks then I will satisfy our customers...

But I felt it is not a good answer per that Sr Manager's response.

PS, I failed. Of course I knew this is not one important factor...