President Bush has said that he knows Harriet Miers “well enough to be able to say that she’s not going to change; that 20 years from now she’ll be the same person with the same philosophy that she has today.” But when considering the case presumably more personal and important to her than any individual case before the Supreme Court will be—whether to serve on the Court—she changed her mind over the course of months. This is from her Senate Judiciary Committee Q&A:

When Justice Sandra Day O’Connor first announced her desire to retire, I was asked whether my name should be considered. I indicated at that time that I did not want to be considered. I participated in all interviews that ultimately resulted in the President’s selection of Judge John Roberts.
When Chief Justice William Rehnquist passed away, I participated in consideration of potential nominees to fill a second vacancy. At some point I understand that individuals at the White House began considering me as a potential nominee without advising me. During approximately the last two weeks before the announcement of the intent to nominate, I spoke with Deputy White
House Counsel William Kelley, Chief of Staff Andrew Card, and the President, and realized that my name was under consideration. I met with the President four times to discuss the possibility of my nomination: September 21, 28, 29, and October 2. I had a discussion with the President on the evening of October 2nd and had dinner with the President and Mrs. Bush. At that time he offered and I
accepted the nomination. The dinner was arranged by the Chief of Staff.