Uncovering the mystery of lost Bitcoins?

In my case I haven't experience something like losing Bitcoins in wallets because I forget my private keys because I am vigilant to every transaction I made and storing my keys so I can retrieve my funds anytime anywhere as long as there is an internet connection. It is really the owners fault of losing funds due to irresponsible handling. Phishing and malwares are not considered as lost because that is hacking activity where funds are intentionally stolen by hackers.