Uncovering the "why not" will reveal a lot of things you need to know when developing a new idea or concept. Innovators should seek, not avoid, criticism and opinions even when it's not what you want to hear. Encourage people to push back and challenge your assumptions. Otherwise you may find out later, you had a good idea, but you were working on the wrong problems.
Objections expose things like past experiences, attitudes, and perceptions. These can be challenges you've overlooked or didn't consider.
When you court objections, don't settle for generic excuses like "it'll never work", or "we've tried that before". Probe deeper, get more details, ask for anecdotes and examples. Challenge their assumptions too.
If you're dealing with a naysayer, just let them spew. Resist the urge to counter objections in real time. It'll only feel like an argument. Revisit your idea with them later, and show them how you would resolve their objections. Don't go looking for a fight. Just consider it research or a "reverse brainstorm".
Some people are just incessantly negative. They use outlier cases and fringe scenarios as an excuse to not do anything. Make them accountable by showing you're willing to address problems while they're just talking about them.
This approach takes some getting used to. After all, it can be demoralizing to hear people rattle off a litany of reasons why your idea won't work. But that's only if you let it. Keep in mind, objections are just problems that need to be solved.