Imagine you wake up in the morning and you feel kinda cranky.  Lots of things happened yesterday, some good and some bad.  You're not quite sure what's making you feel cranky, but if you knew, you'd be able to sort it out and feel better again.  It's pretty hard doing this when you've got all the pressures of daily life bearing down on you - make the breakfast, get the kids ready for school, do the school run, sit through those important business meetings etc.  Wouldn't it be great if you could start the day with none of these pressures on you, with just the minimum you need to function, to allow you to sort through what happened, and work out a way to fix it!
If only life was so simple!  Fortunately, Windows has such a feature, and it's called Safe Mode.