be at the sharp end (of something)

informal To be engaged in the most challenging or difficult part of an activity. Primarily heard in UK. This repair was pretty simple, but now we're at the sharp end—replacing the battery. We're negotiating the payouts to the executives, which, if you ask me, means we're at the sharp end of this merger. Uh oh. You guys aren't even at the sharp end of this project, and you're already running into issues with the data?