I went into my first exam (BEC) not necessarily planning to fail, but expecting it… and I was so relaxed and nonchalant that I believe it helped me a great deal. I had only studied for three weeks and minimally at that. The second week we went to my father's house for Thanksgiving, and the third week I was sick. I mentioned in another thread that I probably studied for 30-35 hours total.
I had no expectations of doing well but I did not want to push the date back to January (I took BEC on November 30), so I figured I would just go in there and give in a try. I wanted to see what the actual exam was like as well. I have always felt comfortable with economics and finance but didn't prepare much at all for the last couple of modules in the Wiley book. Anyway, I went in there feeling no pressure whatsoever. There were a few questions that I guessed outright and others that I made educated guesses, but many of the questions I did know and even seemed rather simple. I thought the written communications were easy as well.
Nevertheless, I left the testing center expecting to not pass, and actually started studying for BEC again the first week of December. I checked my state's website by chance for my score one day and saw “85” and couldn't believe it. That is why I would advise people who feel under-prepared to give it a shot regardless.
I took FAR last month and was expecting to do well… I was much better prepared but simultaneously much more nervous due to those expectations, so the experience (including the wait for the score) was entirely diverse!