It's a funny world. "One" is a round number for some and not for others.
First there was this and now there's this. One piece takes the position that narrowing down a vendor field in a procurement to a single supplier is a bad idea, the other thinks that it's the only way to get the best deal. Both are right I guess, depending on the circumstances. But neither article acknowledges the need to think about why you are where you are and then take the right action.