Integrity in Project Management

A friend was telling me that a young Arthur Anderson was told by his boss to fake some numbers. Anderson refused. He said that an auditor was bound to report honestly, not manipulate the data. In other words, he had integrity.
Early in my own career, I gave my boss an estimate for how much a project would cost. He protested that the numbers were too high, and said I should be able to do the job for less. My team and I had worked very diligently to develop those numbers, and we felt that they were as accurate as we could make them, given that all estimates are guesses that are based on whatever history you have.
The boss gave me a good brow-beating. He said that if the cost of the project (which was to develop a product) was as high as I claimed, he would not be able to get a satisfactory return on the investment. I replied that I could not help him with the ROI, and that I would not commit to a lower number. In fact, I told him that he would have to get another project manager if he felt strongly that the job could be done for less. With that, he accepted my numbers and asked the company if he could do the project with a lower projected ROI than was normally required. They agreed, and we did the job. Several years later, he got out of the market he was in because he could not sell enough product to get the returns required.
The point is that he made a business decision based on what I gave him as an estimated development cost. It may sound like I was being insubordinate to refuse to commit to a lower number. Had I done so, however, it would have made the situation even worse.
It is the responsibility of a project manager to provide estimates that are as accurate as possible and to stand firm on them. Business decisions are made based on what we tell senior managers. If we provide them with inaccurate data or facts, they will make incorrect decisions. It's a matter of having the integrity to stand fast.
As someone once said, "I can always get another client [or job], but once I lose my integrity, that's it. I can never get it back." Do you have the integrity to put your job on the line?