It's interesting that people think there are certain openings you should learn at a certain stage. I've never really understood this logic.

If you're playing opponents of the same strength as yourself, they aren't likely to be any more booked up on the main lines than you are, so you can get away with playing something like the Open Sicilian and get an equal game. On the other hand, if you're playing a stronger opponent, you won't be able to get away with a substandard opening - you'll get beaten up if you play an unsound gambit, and you'll get outplayed if you play something slow like the Closed Sicilian. No matter who you're up against, you will always stand less of a chance against a better player, so don't try to avoid the mainlines! You'll get beaten up along the way, but that would have happened no matter what you played, so what's the problem? If a player is good enough to know enough theory to beat you in the opening of the Sicilian, then probably he would be able to comprehend why a lesser opening isn't as good, and be able to punish it.

Honestly, as white I think the Open Sicilian teaches you how to attack and develop efficiently, and how to defend...and it's sound! I don't understand why anyone would ever avoid the open Sicilian, unless they are already of a certain standard and know that they prefer closed/positional games. Sure you'll get beaten up by somebody who's booked up along the way, but that happens at all levels of play, in all openings. Gambits have theory too

If the Dragon or Najdorf aren't sharp attacking games, I don't know what are!

I don't believe that you should ever avoid mainlines. In fact I think that mainlines exist because they are good, solid openings.

What I would argue, is that the best openings for lower levels are those that conform to classical principles such as development and central control. All of which will lead a player nicely to middle games and end games. The true heart of chess.

That's fair enough. But you can learn about central control by attacking down the flanks as well What I mean by this is that I don't necessarily believe that just because an opening is 'classical' that it is more 'fundamental'. For example, playing a Sicilian type line with ...a6...b5...b4 and kicking a c3 knight away to get at e4 is just as fundamental to chess as playing the Ruy Lopez with white, with Bb5 threatening (in the long term) to pick up e5. Actually it's the same strategy with the same purpose...and the Ruy Lopez isn't even really that principled when you think about it, because white willingly gives up 3 tempi with the bishop in the Chigorin. My point is that I think any good opening takes central control and development into consideration, and that we shouldn't be too caught up with the chronological order in which strategies where discovered.

Of course, you have to know your pupil, and know what works for them. Just speaking from my own experience, I taught myself to play chess through the Sicilian which - as we all know - was considered an unprincipled opening for a long time. And I did get beat up a hell of a lot along the way by white players who knew how to take advantage of the Sicilian's slow nature...but by getting beaten up I learned the importance of move order accuracy, and knowing just how far you can lag behind in development before it becomes fatal. I consider it a bit like playing e4 against a patzer 1...d5 player. If you don't know what you're doing you'll get beaten up again and again, but eventually you'll learn how to make the precise moves, and then the d5 player will never win again

So an opening, in refraining to encourage you to develop quickly, may actually teach you a more valuable lesson about development than a more 'classical' opening. Losses teach us more than wins!

That's my theory, anyway

Yes I think that is an interesting point. Different openings teach can teach you different things. Or the same ideas but in a different way. I agree that losing teaches us more than wins.

But Maybe I would argue that it can be easier to identify the mistakes you make in "classical" middle game positions. With other openings that have unconventional plans it can be harder to spot the mistake you made...I'm not sure to what extent that is true though.

In conclusion I would just encourage players to play widely recognised sound openings. rather than some crazy gambit which only works against morons like me.