Please, never use this metaphor again. This level of magical thinking is just embarrassing for all of us. It's like saying that building a house must be a really fast process, because burning the house down goes really quickly.

Nuclear weapons blow up easily because, for (e.g.) plutonium, "blowing up" is thermodynamically favorable. A brick of plutonium has much less entropy than a giant fireball and an expanding cloud of radioactive fallout. In a thermodynamic sense, the plutonium nuclei want to be fissioned. All you have to do is find a way to coax them out of their metastable state.

A human brain is massively thermodynamically unfavorable. If you put a bunch of proteins in a box the odds that they will self-assemble into Einstein's brain are, literally, astronomically small.

That's why the brain is a miracle and a nuclear reaction is, frankly, pretty commonplace. There are a lot of stars. Stars are easy to explain. Brains are hard.