Silver bullet is a metaphor for an effective and universal solution for any problem. In computing, the metaphor was notably used in Fred Brooks' 1986 essay "No Silver Bullet".
The belief in silver bullets is quite popular in computing. Many computing-oriented people are vocal fanatics of a single programming language, a single operating system or a single design paradigm, that is better than its "competitors" in every context and will eventually make them obsolete.
Since technological diversity is an important idea in permacomputing, silver-bullet type of thinking should be avoided. Instead of putting ideas or pieces of technology in a universal linear order of superiority, one should be aware of different contexts. The strengths in one context may be weaknesses in others. The "best practice" of a specific context may be an "antipattern" in another context.
Permacomputing is not a silver bullet either.