The moment when Chief Brody (played by Roy Scheider) sees the shark properly for the first time and realises, it's bigger than the boat they're using to catch it.
Up to this point it's been a bravado fuelled adventure for the crew of the Orca. As he backs, shaking into the cockpit and quietly utters the immortal line:
We're going to need a bigger boat
Now a ubixquitous metaphor for finding yourself out of your depth and in need of any given scenario. From the boardroom to the building site, you will hear the phrase "we're going to need a bigger boat" muttered when a rethink is required and the realisation that you don't have the tools for the job at hand dawns.