Why Did My iMac Hard Drive FAIL?

Question

I am majorly upset right now.
My iMac 2009, 21.5"  (4GB Ram, 500GB Hard drive) computer that was practically unused since it was in storage for 2 years in my basement while I went out of town on business- suddenly had a Hard Drive Failure for no reason! Since the Warranty was expired on Apple Care, I took it in a Mac store - only to be told by the repair man that the hard drive needed a replacement. He did quick testing, and these were the results:
Ran MRI and everything passed
Reset pram and SMC
Ran storage diagnostics
Proposed Resolution: Replace hard drive
Total cost: A WHOPPING $229.00 plus tax for the hard drive plus labor costs. When I asked if I could just upgrade to a 1TB Hard drive since I was shelling out money anyways, Apple flat-out REFUSED- saying they couldn't put a warranty on a new hard drive, just the replaced one. Sounds like complete BS to me!
Further more, I would like to know how the **** this happened! A few times when the iMac was on the table and running, I lifted it up and clunked it back down a bit rough to readjust it- but it continued to work for a few more days. I doubt that would ruin a hard drive. I own a Macbook 13" that I clunk around all the time, the hard drive has never failed. Suddenly my hardly-used iMac that worked out the box when I first started using it again suddenly has a random hard drive malfunction a week in??? And now I'm out $250.00. I just feel jipped. I thought Apple products are meant to last. Apparently not. The guy said "Well it's a four year-old computer". Yeah but I only used it one year and then it was in storage! So whose to say THIS hard drive won't fail as well?
Why did this happen?

Answer 1

Hard Drive Warning (all makes and models)
Ironically but logical, new hard drives are far more fragile than one that has been working for several months or a couple years. So beware in your thinking that a new hard drive translates into “extremely reliable”!
Hard drives suffer from high rates of what has been termed "infant mortality". Essentially this means new drives have their highest likelihood of failing in the first few months of usage. This is because of very minor manufacturing defects or HD platter balancing, or head and armature geometry being less than perfect; and this is not immediately obvious and can quickly manifest itself once the drive is put to work.
Hard drives that survive the first few months of use without failing are likely to remain healthy for a number of years.
Generally HD are highly prone to death or corruption for a few months, then work fine for a few years, then spike in mortality starting at 3-4 years and certainly should be considered end-of-life at 5-7+ years even if still working well. Drives written to once and stored away have the highest risk of data corruption due to not being read/written to on a regular basis. Rotate older working HD into low-risk use.
The implication of this is that you should not trust a new hard drive completely (really never completely!) until it has been working perfectly for several months.
Given the second law of thermodynamics, any and all current mfg. HD will, under perfect storage conditions tend themselves to depolarization and a point will be reached, even if the HD mechanism is perfect, that the ferromagnetic read/write surface of the platter inside the HD will entropy to the point of no viable return for data extraction. HD life varies, but barring mechanical failure, 3-8 years typically.
Data redundancy (copies) makes all HD crashes inconsequential, an irrelevancy.
There are only two kinds of hard drives, those that have failed, and those that will fail, regardless of quality of manufacture.
Any Macbook or desktop should be idealized as a working platform computer system, containing all your applications, documents, and weekly-use necessary files; and all media files such as ‘big-data’ (music/PDF collections/video/pictures), unless directly needed in the near future, should be kept off the computer and on external storage USB or likewise bare hard drives.
Never consider any computer a data storage device at any time under any circumstance, rather a data creation, sending, and manipulation device. Anyone who thinks data is safe on any computer, even copied upon multiple partitions is making a mistake that will, without fail, strike.
Never backup your data exclusively upon magnetic hard drives or flash storage, nor consider same since magnetic storage degrades over time, roughly 3-8 years, even under ideal storage conditions.