Get used to it...
This one starts with a cliche: Life stinks.
Everyone has bad things happen to them; it's a fact of life. It would be the utmost arrogance to believe that nothing should ever go wrong for us. In fact, I think just about everyone would agree that, from time to time, things don't always live up to our expectations. It isn't the small things that bother us - the weather's not perfect, our hair isn't perfectly in place - those things we could get by with. It's the huge things, the losses and the pain, that make us wonder why.
Why? Why does it have to happen to us?
Life stinks, that's why.
Having already admitted that things sometimes go wrong for us it's not an enormous leap in logic to continue this train of thought into the idea that pain and loss are just as much what life is about as pleasure and happiness. You get them both and, though we like to find patterns in things, it often happens in a wonder of randomness.
Random happiness. Random pain. We never know when it will happen. In fact, we'll often say, after suffering a loss, that we never saw it coming. And if we knew the good that lie ahead, would it be as good?
So, things go wrong for us sometimes and, knowing this, it's easy to see that it is part of living. That said, it's easy to conclude that you aren't here to be happy. Life isn't meant to make all your dreams come true. Knowing this, perhaps we should appreciate the good things all that much more when they do come our way. Perhaps, too, we should understand that pain is as much living as is breathing.
As the Buddhists say, life is suffering.
... Pardon my irony when I say I've been living life to its fullest...