It goes against most of natures to let projects fail – even just one part. We will often go to great lengths to make sure that everything works and comes together for the best result possible. Even if it means ridiculous hours, crazy processes and recruiting as many people to help as needed.
Saving the world too often creates perverse incentives for the team though. The more you do things that should never have been possible the more these situations are going to come up. You end up training people that the impossible can be done on a regular basis. Sometimes the only way to break the cycle is to let things succeed or fail on their own. This means not stepping in directly to save someone else that may not realize that they are in trouble.
This does not mean that you should actively not help – it just means that sometimes you shouldn’t go above and beyond where it isn’t your responsibility. Letting others prove themselves has tremendous value to the business. The more people that exist that can get things done, the better.