[EDIT: see below] During a job interview, when they ask if you
  know something, quickly ask yourself, "Can I learn this on the
  job?" If you think you can, then say "Yes I do". * Since every
  job has a probational period (1st for 3 weeks to see if you're
  not homicidal, and about 3 months to see if you can hack it),
  it's enough time for you to learn whatever you said "yes" to. *
  EDIT: A straight "Yes, I do", if it is an absolute lie, be
  careful. Might be best avoided. What might be better is: "I
  don't know the specifics of what you need for this position, but
  I'm a fast learner and I'll pick up what I need to know quickly,
  as I have comparable knowledge in...[x], [y], [z], etc",
  highlighting transferable skills. I wrote this because I've seen
  too many people who continue to stock shelves (nothing wrong
  with stocking shelves mind you) because they're afraid to try
  something new. They may lack the schooling, but they have the
  knowledge. They may lack the certification, but they're capable
  of the job. But they're afraid because they don't feel official
  enough. They get stopped at the gates of Human Resources without
  realizing there's other ways to get employment that can make use
  of their skills.