Voice assistance has come a long way, but there are still times when even the best of us struggle. On Wednesday, Microsoft CEO Satya Nadella found that out the hard way when his own company's Cortana assistant refused to play ball, live on stage.

At the keynote event of Salesforce.com's Dreamforce 2015 conference in San Francisco, Nadella demonstrated integration with Microsoft's products, praising Cortana's ability to provide voice-controlled analytics.

"Show me my most at-risk opportunities," said Nadella. But Cortana had other plans, instead firing up a Bing search of "show me to buy milk at this opportunity." Nadella gave it another shot, but this time Cortana decided it was time to start reminders. The third time, Nadella gave up using Cortana and quit the assistant halfway through the request.

Eventually, Nadella was saved by help working from backstage, who called up the most risky opportunity in the demonstration account.

It's not the first time a voice assistant has failed in a demonstration. At Apple's WWDC 2015 event, Senior Vice President Eddy Cue struggled to get Siri on the iPhone to recognize a request to "play the song from Selma."

Cortana is available in Windows 10 and Windows Phone 8.1. Versions are planned for iOS, Android and Xbox One. Microsoft has even revealed a prototype car that integrated Cortana right into the windshield. Before Microsoft unveils a Cortana-powered car, let's hope the assistant will have learned a few more tricks.