I've had a hunch for a while, one more about people than Dominion, but now I have some numbers suggesting it too, and those are 100% Dominion.
See, I have a blanket policy of blacklisting anyone who denies one of my undo steps for any reason. Granted, I don't request dubious ones (yes, subjective, I know-- not the point of this post), but as you can imagine, I have a decently long blacklist at this point.
I recently searched the Scavenger Leaderboard to compare it with my blacklist and not a single one of them is in the top 1000 players.
I play a LOT of games, against players of all skill levels, and it's easy to notice that skilled players tend not to deny undos very often. Do I have confirmation bias? Sure.
But referencing my blacklist against the leaderboard with zero overlap is also pretty convincing that denying your opponent an undo step betrays a lack of confidence in your play. That lack of confidence in turn suggests a deficit of skill, but that's to be expected if you create negative play experiences for yourself and your opponent.
So if you're one of these people, holding yourselves back with a toxic attitude toward the game and your fellow players, I want to challenge you to reconsider. Next time you're thinking about pressing "deny," think twice. Grant the step and see how much better your games get, and how much better you get as a player.