user-1: Reversed openings, as in ones for Black that are played by White, have a characteristic that usually main lines for Black are obscure in White, and vice versa. How would this be true, since White is only one tempo up?

user2494: When Black plays a first move, it's usually directly related to White's first move.
1.d4 means White can't play d2-d3, so e4 is more up for grabs, which makes 1...f5 palatable. If White plays Bird's 1. f4, then From's 1...e5 2. fxe5 d6 is promising. White doesn't have that type of reply against the Dutch.
Take the Budapest. 1. d4 Nf6 2. c4 e5, and if 3. dxe5, Black typically goes 3...Ng4 with a long-term view of keeping a knight posted on e5. But if you try that in reverse with Tennison's Gambit, 1. Nf3 d5 2. e4 dxe4 3. Ng5, there's a little less to like about it. In the Budapest given, a knight on e5 has the c4-pawn to target, while that same knight for White in Tennison's gambit isn't as fortunate.
For a long time, we looked at the English Opening like this: If 1. c4 e5 2. Nc3 Nf6 3. g3 d5 4. cxd5 Nxd5, and so on, in a Dragon-Sicilian-in-reverse
way, it turns out that the extra tempo White has is usually spent wondering what to do with the queen bishop. Bc1-d2 was hardly a great use of that 'extra' move. I think the view on this has changed over the years, but you see what I mean.

-1: <p>Reversed openings, as in ones for Black that are played by White, have a characteristic that usually main lines for Black are obscure in White, and vice versa. How would this be true, since White is only one tempo up?</p>
 2494: <p>When Black plays a first move, it's usually directly related to White's first move.</p>
<p>1.d4 means White can't play d2-d3, so e4 is more up for grabs, which makes 1...f5 palatable. If White plays Bird's 1. f4, then From's 1...e5 2. fxe5 d6 is promising. White doesn't have that type of reply against the Dutch.</p>
<p>Take the Budapest. 1. d4 Nf6 2. c4 e5, and if 3. dxe5, Black typically goes 3...Ng4 with a long-term view of keeping a knight posted on e5. But if you try that in reverse with Tennison's Gambit, 1. Nf3 d5 2. e4 dxe4 3. Ng5, there's a little less to like about it. In the Budapest given, a knight on e5 has the c4-pawn to target, while that same knight for White in Tennison's gambit isn't as fortunate.</p>
<p>For a long time, we looked at the English Opening like this: If 1. c4 e5 2. Nc3 Nf6 3. g3 d5 4. cxd5 Nxd5, and so on, in a Dragon-Sicilian-in-reverse
way, it turns out that the extra tempo White has is usually spent wondering what to do with the queen bishop. Bc1-d2 was hardly a great use of that 'extra' move. I think the view on this has changed over the years, but you see what I mean.</p>
