I've heard that one too. If you're getting every job you're too cheap, if you're losing every bid you're too expensive, if it's half and half you're on target.
Just for the record, not really half and half. If you are bidding in a market where the customer gets 3 or 4 bids, then you shouldn't get more than 25-35% of the jobs if you use statistics. In my opinion, you need to figure that a certain percentage are going to go to idiots, so anything more the 15% and you are probably too low. So then take that figure how many dollars of work you need to generate how many dollars of money you need to be "successful" divide by 15% and you will know how many dollars you must bid.