get off track
1. Literally, to lose one's bearings or course of direction. It was only after an hour or so that we realized that we had somehow gotten off track during the storm.
2. By extension, to lose sight of or be distracted from one's goal(s); to become unfocused; to stray from the central topic, issue, or subject at hand. I tried to keep everyone's attention on the few key issues that needed to be addressed, but we kept getting off track with general complaints and asinine suggestions. We wanted to have the product released by the early spring, but we got off track with a number of technical issues.