Usually it takes a great mind and intuition to realise what the matrix is without assistance. However it can also happen for other reasons. For Dan it happens as a result of him pushing himself to his physical limits in an attempt to prove the world wrong in their accusations of drug abuse.
When his muscles fail during a race, Dan keeps going. He pushes his mind beyond the physical restrictions of his body and it shows him the truth - that his body as he knows it is not real. Part of the series of animations making up the Matrix companion piece `The Animatrix', I saw this as a stand alone piece recently at a festival of shorts and animations and it stood out as being of a rather more basic visual style than some of the other shorts.
The plot took a minute to settle as it messed around with back story but, once it got into the race it became more interesting as I realised why the runner was able to learn of the matrix (as described above). The animation is not quite as good - by which I mean, not to my tastes. The bleak shadowy effects are interesting but at times it was a bit too extreme. The cross over into the real world was well handled but the touches added to the agents didn't work for me and over-elaborated on characters who were perfect in the film simply because they are meant to be unmemorable and blend into a crowd.
Overall this is good as it is interesting but it is not the best of the series. It is worth seeing once simply to expand on the Matrix experience but it could have used a bit more substance in place of the athlete's back story which was unnecessary and unused.