As described in this post, superposition is a key aspect of quantum computing. However, people mistakenly assume that superposition is all that is needed.

A given quantum memory register  (RAM) , may contain the output of your operation. A careful sampling from this quantum RAM, may contain the correct answer. Odds are overwhelming that it will NOT.  In fact, there are many more possible non solutions than there are solutions (to just about any problem that is solved using quantum parallelism – i.e. quantum superposition.)

What is needed is that a lot of the non solutions interfere with each other and disappear. And also, for the actual solutions to constructively interfere and amplify the amplitude. For this to happen, the problem has to lend itself to such a co-operative interference of amplitudes.

Shor’s Algorithm, devised by Peter Shor of AT&T, is one such problem.  More on this in another post.