I meant it as Bayesian evidence. (updating P(Arbitrage works) down on Bester regretting means updating up on him not Regretting)

Plus, this is stronger evidence for us than for Harry due to Conservation of Details and the recent disclaimer by EY that there are no red herrings, and that simple solutions != bad solutions (and in fact, the opposite is usually true).

ETA: Also, Bester probably thought about it more more than a few seconds, at least the first time he saw it in Harry's mind - Remember that he didn't just see those Ideas/secrets, he's also seen key moments of his previous conversations.