On preferring the worse feeling
“Doubt is not a pleasant condition, but certainty is absurd.”
Voltaire concedes the first half without argument. Doubt is genuinely unpleasant — it is unrestful, it makes decisions slower, and it offers nothing to stand on.
His point is that the alternative is not a better state but a false one. Certainty feels like solid ground because it has stopped checking, and the comfort it provides is exactly proportional to how little it is now looking at. Between an uncomfortable condition and an absurd one, he takes discomfort.