King John was not at all unlucky. He was lucky alright. He had a famous pedigree with Richard the Lionheart as his brother, and he reigned 17 years. Just as the previous poster stated, he was just plain dumb in his decision-making process. To that, I will add that King John was also lazy. He continously made wrong decision after wrong decision, even choosing his mistresses!He never took one second to second-guess decisions, and (on top of it all) he signed the Magna Carta. I say this is a monarch with no common sense at all!
I guess you could say he was unlucky because he was the younger son in the family and because his parents belittled him and preferred Richard, but it's hard to say that he wasn't a bad king as well. It seems to me that he was too greedy and ambitious and that, in addition, he wasn't a good enough politician to get away with it.
As soon as Richard was captured, John declared him dead and set himself up as king. That was not unlucky, that was dumb. Another dumb thing he did was to pick a fight with the Church by rejecting their pick for Archbishop of Canterbury and then seizing all the Church's property after the Pope interdicted England.
So it seems clear that he did some pretty dumb stuff. And it is clear that he wasn't good enough at politics to keep enough of the nobles on his side to prevent them from imposing the Magna Carta on him.
King John was unlucky. He wasn't sensible either. It was a mixture of both, I suppose. I guess he was trying to prove his resilliance so he didn't stop trying to coquer the French. He was unlucky he lost, but it was just kind of hopeless that he still kept investing in the invasion of France instead of just giving up. I know, I know. Quiters never win. But I think it's better in this case if he just gave up.