i give 50-50; because it varies from person to person - situation to situation;

But, I would say that if you like any girl and feel that her character suits to your character, go ahead and discuss with your parents. If they don't agree, try to convince and marry. I am totally against run away marriages!! These days, I see very rare where parents don't agree to your wish!! I also agree that there are some parents who don't agree - then I can't say what you need to!! It depends on your situation; If you are 10000% sure that the girl you like is going to be an ideal match, then there would be no other option of marrying her; though it's against the wish of your parents. But, before that, you need to try to convince your parents 100000000%.

Your parents definitely know your character and I'm sure they can judge very well...