When the company needs an out of the box solution, do you believe your team will have the skills to find that solution? Leaders need to encourage creativity in their employees and give their employees opportunities to grow their creative skills.
But how do leaders go about doing this? During brainstorming sessions, allow your team members to throw out any ideas they would like. It could be anything from the simple to the ridiculous! Brainstorming sessions aren't the time to negate ideas, even if the idea is seemingly impossible. If you start rejecting ideas that don't meet your standard, people will feel less inclined to offer up other ideas in fear of being rejected.
If your team member comes to you with new ideas, tell them you like the idea. If you don't see how an idea could happen, ask this team member to write up a plan and send it to you. Any good behavior should be encouraged and complimented whenever possible. This way, your team starts feeling that their ideas are valued. They will also trust you enough to tell you future ideas which could be a great opportunity for company growth.