Why is the sicilian so strong at all levels?

In the databases, in amateur or master games, the sicilian defense is the only opening in chess that black wins the same or even more than white, at all levels. No other opening does that. Ninzo-indian comes close, but still far from that power (and can be avoided).

What is the reason ? In my games I see that black has a huge positional advantage with the two pawns in the center and the plans are pretty straightforward, meanwhile white has to calculate variations to attack and has no "thematic" plans. As white you have to think a lot to where put the pieces, and black has clear plans. Nf6, nd7, bb7, d5 etc.

But is that the only reason ? the sicilian being a lot easier to play as black than with white ?

"All levels"??? 

Have you seen beginners try and flounder there way through it?  Its scary...and laughable..all at the same time.

All players I have encountered follow the plans for the sicilian, putting pressure on the queenside and on the e4 pawn.

I run into this so often im at the point where I hope they play the right move, since its not even fun anymore.

The Sicilian is not that strong at super gm level, as time goes on it's being considered more and more a (teeny weeny) bit dodgy at the elite level, it's only used there if black really wants to win. 

I also get the feeling that at the club level a lot of players devote an artificially large amount of time to their sicilian defence. I'm not saying this accounts for all of why the Sicilian is like this but it's a factor to keep in mind. 

What's the point of your post? It just agrees with the OP and then you mention the contrary. If the sides were flipped maybe your comment would make sense.

I’ll face the Sicilian over nimzo-indian any day

Back in the day it was the most analyzed opening because people were playing and winning with it. More data fine tuned the opening. For instance the Marshall Attack was developed and the preferred method for white to attack the Sicilian for over a decade in the 1800s. Enough data was collected for the Sicilian to defeat the Marshall Attack and so white players had to start over.  Now with chess engines, maybe a new opening would be found that is better for black.

Are you sure the Sicilian is the best at all levels?

I'd imagine at the beginner-intermediate level, the Sicilian would do quite poorly for black.

As someone who plays the open Sicilian as both white and black, I have to say that the white side of the Sicilian is more comfortable and easier to play for me.

Okay, I think I've worked it out. It all comes down to one move: Bc4.

When white plays Bc4 too early against the Sicilian, it gives black a decent advantage, and low rated players will often do this:

If white can resist the urge to play Bc4 too early, then white should do very well against the Sicilian, especially at the intermediate level.

If you're looking at master-level databases, you might be reading them wrong. White wins approximately 10% more than Black in the Sicilian.

It's true, though, that the Sicilian is the most popular response to 1.e4.

The only exception is when we reach the upper Grandmaster levels. At 2600+, GMs begin showing a slight preference for 1...e5.

At the 2700+ level, 1...e5 becomes even more popular. It moves from being a "slight" preference to a "clear" preference.

So we might conclude that the Sicilian is the best response to 1.e4 until you hit the 2600 level. Then 1...e5 becomes the better choice.

So basically what I said except I also added how the Sicilian is also often used if black must win. 

Also saying "White wins 10% more than black" - has no meaning. White is naturally going to win significantly more than black. What matters is the score of white vs black, Wins 10% more than black doesn't mean anything unless you also give the percentage of draws. 

Well, yes, it doesn't say much. But I was correcting the OP, who suggested, "... the sicilian defense is the only opening in chess that black wins the same or even more than white".

Saying that White scores 10% better than Black, in the Sicilian, is a big difference from saying that Black scores "equal or better".

If Black was shown to score equal or better than White on move 1, it would likely be huge news in the world of competitive chess.

Even when i was active in chess and seriously studied.  I never played the Sicilian.  Its to much to learn and remember.  A couple years ago i found a rare line in the Taimanov that is fun to play, and doesn't require a lot of theory.  Compliments of an Igor Smirnov course.

7% in master databases. All other openings white wins more than 10%

I did two searchs.

2300> (masters), black wins 27% and white 33%
All games, from all levels, black wins 36%!!!!!!!! and white 37%

So, the "advices" were actually wrong. Black side is easy to play (scores more in low levels) and it's white who needs to "Learn" more chess in order to get better results.

Not sure where you are getting these stats from but it seems massively inaccurate.

White has first move advantage and that's end of story, you can't argue black is better, not only does that defy all common sense and logic but it simply isn't backed up by statistics.

My sicilian games (no theory like just the first 2/3 moves are theory) are 50% winrate compared to the POWER OF THE BIRD, the bird's eye opening that got me +250 points as white in a bit over a week.