As product managers we are charged with being the voice of the market and being in tune with what users need and are willing to pay for. To know what potential customers want and will buy, we can simply ask them, but experienced product managers know this only gets you so far. People answer the questions you ask them; not the ones you don't ask them. They often tell you what they think you want to hear. Occasionally they lie. A good facilitator can sometimes break through these barriers and extract the truth, but it gets harder as the products, features, and solutions become more disruptive. This is particularly true for technology products. Potential customers will reliably tell you they prefer the white BMW over the green one, but try asking them about BMW's iDrive system when they've only used old, analog, discrete controls and it's a whole different scenario. Good luck with that.
To outwit our users, we product managers take a different tact. We don't ask them what they want; we watch them. We experience their worlds, understand what frustrates them, and try to gain insight into product gaps that force them to a work-around, substitute, or completely different product. As Yogi Berra said, "You can observe a lot just by watching." Armed with these observations, our development teams will come up with clever ways to address the problems.
This takes us back to Fisher-Price. When the users are babies and toddlers, there is no choice other than simply observing them. No questions to ask, and no answers to lead them to. You're forced to see what makes them tick and what frustrates them in a pure, unfiltered way. Does this make them the ultimate end-user? Perhaps.
Next time you visit a customer for a day-in-the-life-of visit, take a page from Fisher-Price's book: imagine your user in diapers, bring along some Goldfish crackers, and keep your mouth closed.