It means you are not legally allowed to lend them or sell them, even if you lose the original DVD and even though you did have the right to lend or sell the original DVD.
IANAL, but even if we assume the act of backing up a DVD to hard drive is legal, it's not clear to me how one could legally use the resulting copy without somehow circumventing CSS.
And with only narrow exceptions that probably don't apply here, this act of circumvention violates 17 U.S.C. 1201(a)(1)(A)[1] unless the copyright owner has authorized the process (as they do with licensed playback devices and software).