A wagon driver's olam habo

There is a story about three tzaddikim who were once travelling in a wagon. By and by, the wagon-driver became drunk, and fell asleep. The horses began running freely, and all the passengers were in great danger. Their very lives were in jeopardy.

Just then another simple wagon-driver passed by, and, realizing the danger, risked his own life to jump onto the errant wagon and regain control of the horses. His efforts were successful, and the tzaddikim owed him their very lives.

Years passed, and the 3 tzaddikim were once sitting together, and they decided to use their ruach hakodesh to ascertain what happened with their benefactor. They determined that he had passed away from the world some time ago. Upon his arrival in the Heavenly Court, his defending angels recounted the story of his saving three Jewish lives. Anyone who saves even a single life is considered to have saved an entire world; - how much more so in the case of this simpleton who saved the lives of three tzaddikim, who would eventually influence hundreds of thousands of Yidden.

This act stood in his merit, and it was decided to award him olam habo. However, olam habo consists of enjoying G-dliness, something which is dependent on the vessels that we created through Torah and mitzvos. 
This simpleton had no means of appreciating or benefitting from olam habo. Thus it was decided that his only possible reward would be to place him in olam hadimyon: He was given the illusion that he was driving the most magnificent wagon, being pulled by 4 large and powerful horses, on a road that was straight and devoid of any obstacles or potholes. And this went on endlessly, because this was the extent of what this simpleton was able to enjoy.

(When the tzaddikim who were his beneficiaries saw the state that he was in, they found a way to do a favour to his neshomo, and elevate it to a level of gan eden)