But

But what if it wasn't true?
But what if they were all lying to me?
But what if I made a mistake?
But what if I failed?
But what if I got hurt?
But what will people say?
But I'm too tired...
But it's too hard.
But it's boring.
But I don't feel like it...

Didn't they teach you in school never to start a sentence with 'but'?