It usually necessitates a seed. The seed in crystallization is sometimes a small particle of that same crystal. Putting a bit of the pure substance into a solution will cause a chain reaction where the crystalline form of that particular compound will settle out. Another way of precipitating crystallization is to scratch the side of a beaker with a glass rod. A few scratches and suddenly crystals start to appear.
Scratching seems like a very odd way to get crystals to form, but it works.
Using a shout or a blow is an odd way to get someone to come to realization. You would think that explaining might be more helpful. As it happens, explaining is the least effective way of bringing someone to realization. Explaining creates an intellectual understanding. I am talking about realization.