I think it is really hard for certain people to admit that there are multiple ways that lead to the goal and that those other ways (not their preferred ones) are probably just as valid. And when the choice is made not to take their preferred way they turn into net negatives because now they are going to prove their way was better by sabotaging the alternative. This can wreck projects quite handily.

The best managers build consensus and try to avoid people digging in behind 'their' solutions. This is hard work.