Thinking forwards and back is a strategy for analyzing problems there is no apparent solution for.
Determining the solution starts with identifying the current state, the future state, and the gap.
The current state is the starting point, the situation that you want to change.
The future state is where you want to end up, the situation where the issue is solved.
Thinking forward is determining how the current state can get closer to the future state. This could be overall or specific parts of the current state. Either some parts of the current state can be replaced with the future state or the whole current state can be moved forward.
Thinking Back is determining what in-between state would look like by working backward from the current state. What does the situation look like when the last step is taken towards the future state.
Going back and forth between the two perspectives gives you a greater chance of solving the problem.