WARNING: KEEP EXTRA SAVE FILE ON USB-STICK

Various people, on different console types, have experienced freezes, glitches, or game-breaking bugs. Indeed, it is possible that your entire save game can become corrupted, forcing you to restart the entire game, possibly losing tens of hours of gameplay you're never going to get back. It has happened to me personally as well.

Konam[Subsistence] is to blame for putting out a game that has not been properly field tested, and unfortunately some developer decided that you can have only ONE save game available for Metal Gear Solid 5 normally. It is thus advisable to keep at least one additional save game available on a USB stick at all times (especially if you don't have online console options that do this for you).