Definition:
Reverse planning works first by legitimizing idealistic, ‘ridiculous’ ideas, and then gradually working back towards the feasible. This prevents ‘silly’ ideas being thrown away because you cannot see how they might be achieved.
If you plan forwards, there are many possible futures and it is easy to lose your way. If you start at what you want and work backwards towards now, then there are far fewer paths as you see what is required.
It is a proactive strategy aimed at preventing procrastination and helping to diminish those feelings of being overwhelmed.
Further Reading:
Book: Disciplined Agile Delivery by Scott W. Ambler and Mark Lines