Martial art is not useful to most women?

Can a small woman after 1-2 years of martial art practice fend off a big male ailant? I don't think so. Even with superior techniques, will she has the chin to take a lucky punch from a big guy? I know there are women out there who can defend against a big man but only a handful of them, not the majority. My advice to women are to be alert, beware of your surrounding, try not to be alone, martial art is only secondary. Am I right?