If you choose not to decide...

...you still may get away with it. Patrick Brady has run a successful Tekumel campaign in London for years, under a scheme where he allows his players to decide what system they want to use to describe their characters. Some of his players use GURPS, in great detail; others are all but diceless and may never have seen their own character sheet.

I would think it would be kind of confusing for the GM to shift gears (and what does he do if some loon wants to use, say, the Lace & Steel system and insists on slinging playing cards around, or something) but it has worked well for Patrick, so it just might work for you, too.

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