Just ask Intel about pentium floating point calculations, or Microsoft about the Windows calculator. If something stops working, then something has changed. Figure out what changed, and you might figure out how to fix it. This applys to more than just computers. Never assume you're right.
Nobody is perfect.
Never assume you're wrong. See number 4. Never assume that just because something should be true, it really is true. Hardware people always blame the software. Software people always blame the hardware.