"To raise a corps of a hundred thousand
A thousand pieces of gold will be spent each day."
The second chapter of the Art of War begins with Sun Tzu laying out some basics about materials required to wage war. This kind of thing happens quite a bit throughout the book and it can be pretty distracting for Project Managers because our brains have been conditioned to start tracking these as requirements that we'll have to obtain at some point. The run up of all these requirements leads to the statement about the rate of gold per day and the fact that you can't even consider getting an army until you have that covered. The point of all this is to show that in war, there is cost, and that before you can start on the things you think you need to obtain (people to do the work), you first have to account for a whole bunch of hidden costs that you need to address before you go get people.
Bottom line...whether it is war, or a project, getting things done is expensive and there are going to be things that are less obvious or sexy that need to be covered. Before you take anything on, make sure you have a firm grasp of the cost.
"The cost of an interpersonal Challenge is primarily an emotional one. Nonnegotiable conflicts can be very painful, since success generally comes through ending the relationship or changing ti into a very different one. Therefore, careful evaluation and acceptance of the emotional costs of your Challenge are essential to your success."
For Sun Tzu, the cost includes the lives of the soldiers and all the people who are going to have to work so hard to support them. While most project managers are not normally putting team members into direct mortal danger, the cost of the project may mean other projects do not get done... and depending on what choices are made, the business or company could be at risk, which does pose a direct threat to people's ability to work and earn a living and places them in harm's way.
We need to understand the cost of what we take on and what the ramifications of what we are doing are so that we can make responsible, informed a choices while managing the project.
Quotes are taken from The Art of Strategy by R.R. Wing