I am living testament to this.. i have blagged my way into several jobs (had some knowledge but not the qualifications required) and have done pretty well for myself learning as I go. I always say "Just treat me as if i know nothing, I won't be offended, i want to learn the way you do things here" and employers/managers seem to love that..

However i must stress the fundamental knowledge was essential. along with an interest and desire to learn.