This article is from the Martial Arts FAQ, by Matthew Weigel firstname.lastname@example.org with numerous contributions by others.
In short: NO.
First off, while many people enter the Way of the Martial Arts trying
to be the deadliest people in the world, it is not true that the final
objective of most, if any, Arts is this. Many Masters say that the
best battle someone can win is one that he doesn't fight. Most
martial arts are not designed to make you an instant killer.
Secondly, don't expect any miracle to come down on you, any light to
come through your window in the night and make you the most skilled
fighter- it all depends on your dedication, on your objectives, and on
the amount of training you get. Any school that promises to teach you
to be an "expert" in less than two years (at the lowest minimum) is
probably a scam. General net consensus seems to be that results can
be seen within a few months but the elusive "MASTERY" is the product
of YEARS and YEARS of dedicated work. Don't be fooled by false