Berkshire Hathaway has no mercy, if you do not deliver value, if your bottom line is not as expected or better you are gone. In a snap. There is no prisoners here. In 2009 we had shut down 100 operating units, you lose money, you are gone. Make sure you make money and you'll be fine. BH is a good company to work for, if you are talented and hard working you can have a good career here, but if your unit is not performing well you are out of luck and you will be eliminated - some times people transfer but that's very rare. The most likely scenario is that the unit including you will be eliminated.
sometimes working hard isn't good enough... gotta have some connections as well