I've never used or even seen Williams around here... but maybe I can help!
Are you getting enough soap on your brush? Keep swirling and swirling and swirling until you have this thick heavy dry cream on all the tips of your brush, and even filling in a little bit inbetween the tips.
Another thing to look out for is if you are adding enough water. There is a point where it can be dry and still bubbly and thin. Oddly enough. Adding water will start to absorb into the soap already loaded inside the brush and spread more and more lather in your bowl or where ever your building your lather. As long as its not runny like soup or gravy... then it is not yet at that tipping point of TOO much water. Its kinda hard to tell unless you go through the whole process in practice. Starting off as dry as possible, and adding a few drops at a time until you go from bone dry, to perfect lather, to a watery mess over and over and over again.
I suggest what a previous poster said, check out mantic's vid on building a lather if you have not already. he does an excellent presentation and explanation of it all. Remember that his brushes are most likely better then what you and I are using... so you need to load your brush with more soap. It will take longer to load and to build lather then he will. Also, skill comes into play greatly during all this too!
My Shave Den Equipment List - http://wiki.badgerandblade.com/User:Koss