I mean the trinity test didn't fizzle out. Seems like most bomb tests went off without a hitch first go. Again these were mostly teams of physicists under 30 years old doing this work. I would guess "how I would build my nuclear bomb" is a pretty ever present thought experiment for nuclear physics grads. And if you were empowered by a state to solve this problem with all the resources states typically devote to their own nuclear programs, it just won't be a matter of "if." Once again, no one who walked down this path has failed really. The secret sauce is probably boringly simple and readily apparent in small scale experimentation.