I think just because if you didn't do certain things, you wouldn't have met someone or done something. It's like there's a path but you don't know it at the time.
Like, I wouldn't have met my dp if I had got the first job rather than the second. I would have been made redundant if we hadn't moved exactly when we did (had no idea company I was working for was going under and nor did anyone else I just seemingly went at the right time) I wouldn't have got the great job I've got etc etc...
You could put it all down to coincidence or me just being soppy but I do like to believe (possibly for my own comfort?) that fate does play a part.
I'm sure a lot of people will think it's a load of old rubbish though.
I'm undecided about karma.