I probably only "know" about 20 percent, but can make educated guesses on another 30 to 40. Makes me seem smarter than I really am. I have a formal education in ERP and accounting and databases. I've only been doing implementations for a few years, but they have been crash courses virtually every one where I have to pick up some other part to it.
I respond much of the time with educated guesses because I figure a guess is better than not responding. If I'm right, great, if I'm wrong, oh well, it was only a guess.