So lets look at a couple buying a car. Let's say one partner is busy finding information about cars and the other partner is deciding which of three cars to buy. One is in Stage 1. The other is in Stage 3. When the car topic comes up there could be a conflict.
Successful couples figure out how to peacefully get on the same stage.
Usually it's best to go back to Stage 1 or 2 in problem solving. More information is usually better. Then again, there are times when action needs to be taken. So work with your partner to get on the same stage of problem solving. You might come up with better solutions.