Other things that Tim might mean when he says 20%:
Tim is being dishonest, and believes that the listeners will update away from the radical and low-status figure of 20% to avoid being associated with the lowly Tim.
Tim believes that other listeners will be encouraged to make their own probability estimates with explicit reasoning in response, which will make their expertise more legible to Tim and other listeners.
Tim wants to show cultural allegiance with the Superforecasting tribe.
Other things that Tim might mean when he says 20%:
Tim is being dishonest, and believes that the listeners will update away from the radical and low-status figure of 20% to avoid being associated with the lowly Tim.
Tim believes that other listeners will be encouraged to make their own probability estimates with explicit reasoning in response, which will make their expertise more legible to Tim and other listeners.
Tim wants to show cultural allegiance with the Superforecasting tribe.