Congruency is trying to find a balance between mismatched pieces and a whole set by the same designer. While, some similar pieces are great, it is more popular and well-rounded to have different pieces brought together to form an interesting and fun space. Congruency comes into play best by matching two or three pieces from the same designer in the same space or throughout the entire building for a flow that feels natural. For example, if you have an Arne Jacobsen table, its popular to accent it with an Arne Jacobsen chair. This is great for the overall flow of the room and tends to work out in a cost-effective way.