A spore which comes in contact with the right nutrient soil under the right circumstances will germinate. This will start with the forming of the primary mycelium. This mycelium is often called 'monokaryotic' mycelium.
When this mycelium comes in contact with another compatible monokaryotic mycelium, secondary mycelium will start forming. This secondary mycelium is called 'dikaryotic' mycelium.
Dikaryotic mycelium is therefore the result of the joining and melting of two sorts of monokaryotic mycelia, which then proceed as one. Only the dikaryotic mycelium will germinate mushrooms. The monokaryotic mycelium on its own cannot grow into a mushroom. The chance that only monokaryotic mycelium will grow in your substrate is generally very small.