As the chain is only as strong as its weakest link, so a group is only as smart as its strongest member.
No matter how poor his/her idea is, the loudest, strongest-willed person in the work group will get his/her way over any smarter idea. Anyone who knows better but is too timid to speak up will not be able to propel your group project in a positive direction.
It's not enough to surround yourself with smart people.
The smart people need to be the ones in charge.