The Causes of Notebook Hard Drive Death
See the companion article: The Easy Way to Replace a Dying Notebook Hard Drive.
Most notebook drive failures fit into two categories: Heat and physical failure. First, heat is unavoidable, it is not possible to mount three 120 mm fans on a notebook and still have it be a notebook. Second, notebook drives are not designed for 24x7 operation, it's more like eights hours a day (8x7) typically.
According to many studies, the hotter the drive the higher its chances of failing. According to a study by Fujitsu, see the graph below, an average 2.5" notebook drive cooled to slightly above body temperature should last for one million hours before failure. In other words the drive should exhibit a mean time before failure (MTBF) of 1 million hours. Wow! And while notebook drives do run pretty cool these days, the majority of notebooks run exceedingly hot internally due to heat from other components like CPUs and graphical processors. Fujitsu's postmortem analyses show that high temperatures will cause "electron migration" in semiconductor parts, leading to spontaneous failures. The drive head element is the smallest and most sensitive to heat, but, heat can eventually cause failure in any part of the drive.
While heat can cause controller board failures, human stupidity can as well. I can attest to this. During a routine drive swap, I accidentally dragged the bottom of a hard disk across some bare metal and lo-and-behold, a healthy handful of little circuit board bits came rattling off, like a Nerd's candy, onto the table. Ouch. So be careful. Luckily most new notebook drives these days have the electronic bits on the flip side. Unluckily, this also means those electronic bits are facing into the hottest part of the drive.
Some of my oldest hard drives used some kind of grease in the spindle motor bearings that, if repeatedly cooled and heated, over time attained the consistency of bubble gum. Newer drives use all kinds of modern technologies like fluid dynamic bearings, but the moving parts of a drive's motor will fail eventually.
A notebook hard drive can take plenty of knocks, but, a good hard knock while the drive head is busy working the platter can cause the head to smash down into your data. While this may or may not cause the drive to totally fail, it's not a good thing.
A hard disk is responsible for remapping bad sectors onto good ones. The hard disk keeps spare good sectors around, but eventually one of two things can happen. All the good sectors are used up or the drive's internal mapping table runs out of room. In my experience, notebook drives usually fail long before they run out of remappable sectors.