Based on SMART data, you can judge the health of a disk, at least that is the idea. If I, for instance, run sudo smartctl -H /dev/sda on my ArchLinux laptop, it says that the hard drive passed the self tests and that it should be "healthy" based on this.

My question is how reliable this information is, or more specifically:

• If according to the SMART data this disk is healthy, what are the odds of the disk suddenly failing despite this? This assumes the failure is not due to some catastrophic event that impossibly could have been predicted, such as the laptop falling down on the floor causing the drive heads to hit the disk.
• If the SMART data does not say the disk is in good shape, what are the odds of the disk failing within some amount of time? Is it possible that there will be false positives and how common are these?

Of course, I keep backups no matter what. I am mostly curious.