Wall Street dealmakers are the ultimate optimists. Ask them how mergers and acquisitions activity is going, and they’ll cheerily say they’ve never been busier. But now that answer comes with a crucial caveat: it’s tough getting my deals closed.

“I have a couple of gigantic deals in the pipeline but I’m struggling to make them land,” complained a top banker at one of the boutique investment banks. Another adviser lamented how five of his transactions collapsed days before they were due to be announced.