How to know how good an opening/defense scores? I play Philidor defense, Lolli attack, Fried Liver attack... Other people choose to play well known openings/defenses, so i decided to ask the following questions.

Everyone learns the Najdorf defense because it scores well. (or because Kasparov and Fischer played it). The Philidor isn't as popular as other defenses on the other hand. I have a few questions about that:


if you wanted to know how well an opening/defense scores, is there an online database that  keeps track of all the games ever played and gives you the overall rating of an opening by calculating the average score, or do you take for granted what other players told you?
How to know if the Najdorf for example is a good opening, maybe Fischer and kasparov won, because they are good players, not because the opening is good. Same question about bad opening and defenses, I mean in the middle game if the player is bad, no opening will let him win, I mean how much can you memorize? How many variations? At some point you have have to rely on your intelligence.
Don't good openings become bad opening when they become well known? I mean lets use the Najdorf again as an example, because everyone wants to learn it, it is so well known, doesn't that make it a bad opening? The opponent will be well prepared for it.
And lastly, is it better to play openings/defenses that score well (French defense. Indian etc..)  or is it better to play an opening that is not well known and that your opponent didn't learn?
if you decided to know how good an opening/defense scores, is there an online database that keeps track of all the games ever played, or do you take for granted what other players told you?


For instance if you buy Chessbase, it will deliver a big database with some games. There you can look up for the openings, which were played by the big players. I like to hear and take tips from my trainer, rather than believing in some game from two players with > 2400 Elo. They play completely different, than most of the players. You don't really understand their plans and moves, unless someone comments the game and explains everything. They are not fighting for pieces / pawns, they just fight for one square, which is weak and then in the end-game they will win it eventually, because of this one little weak square.


  How to know if the Najdorf for example is a good opening, maybe Fischer and kasparov won, because they are good players, not because the opening is good. Same question about bad opening and defenses, I mean in the middle game if the player is bad, no opening will let him win.


Fair enough question. If the opening isn't good, wouldn't someone else beat them there (some other good players or an engine)?

The last point is also true. I had many games, where I dominated in the opening but lost it in the middle / end game.


  Don't good openings become bad opening when they become well known? I mean lets use the Najdorf again as an example, because everyone wants to learn it, it is so well known, doesn't that make it a bad opening? The opponent will be well prepared for it.


That's partly true. If your opponent is prepared, you have to be prepared too, but this doesn't mean that it is a bad opening. Especially in Najdorf there are so many variations, you have to know them, when you want to play it.


  And lastly, is it better to play openings/defenses that score good (french defense. indian etc..) or is it better to play an opening that is not well known and that your opponent didn't learn?


This depends on how / what you want to play. I like to play some aggressive stuff. I used to play French defense, but it wasn't my opening. I was losing nearly every game, then I changed to Sicilian and now I win about 25%, draw about 50% and lose about 25%.

If you play something that's unknown, your opponent could still beat you in the opening, because he knows how to play chess (maybe he is also better) and will just spend some time during the opening and analyzing it.