Why knights before Bishops?

Explain plz for levels 1000 ,1400, and 2000 the reasoning behind this knights first principle

(p. 43)

Something that has been written endless times in chess opening literature is the

guideline 'knights before bishops'. Really this piece of advice is simply a continua-

tion of the first conclusion above. The point is that it's usually more immediately

obvious where the knights want to go, whereas the bishops have more choice and

their ideal posts may only become apparent later on.

Emms, John. 2006. Discovering Chess Openings: Building Opening Skills from Basic Principles. Guildford, CT: The Globe Pequot Press.

Yup, that's the "official" main reason, and easily the most valid one. Good quote, Sqod!

I can't back this up with a reference like the above one, but I remember both John Watson and Mihail Marin also have pointed out that long-range pieces like the bishops can exert an influence from their initial squares, so there are cases where they actually don't need to be developed (soon).

I see thanks

Put a pawn in the center in your first (or few first) moves might have even more exceptions 

its about gettingh yhour king to the othir side man

https://www.chess.com/members/view/Lenny_Bongcloud

A Knight on f3 controls some nice central and side squares that can be used for attacking: d4, e5, g5, h4

A lot of cheapo attacks on the King start with a Q to h4

and it's out of the way of the Bishop.

knights before bishops is just something to tell kids so that they actually think for half a second before they make their crappy moves instead of making the first move that pops into their heads

I was thinking e.g. pirc, KID, Nimzo, QID, Grunfeld... I guess grunfeld is 3...d5 though.

But yeah, it may be a really high % like that.

only the knights can jump over pawns. still I often played the bishops opening, but more often 1.nh3, 1.nf3 or 1.na3, but not a fan of 1.nc3 as its too old-fashioned looking.

Only the hippo and hedgehog come to mind as openings that don't have a pawn in the center for a very long time. And c4 in the hedgehog so... that only sort of counts.

So yes, all other openings are doing something in the center... but not always in the first few moves.

Because you are basically fighting for the center

It's just a general rule because it is harder to maneuver your knights compared with the bishops and your knights also do a better job of protecting the squares around your king but of course there are many exceptions.