Why does nearly every opponent move a knight 2nd/3rd move?

What's wrong with f5? I want to take my bishop out, move my Q behind it and do long. According to analysis, f5 is a slight inaccuracy but nothing extraordinary. Idea that it weakens something blunder-like is delusional. It is more like a litmus paper to detect Q abusers.

The move is not good, but this is your problem and since your ranking is better than mine... I was just pointing at the fact it can't be considered "normal". Never heard about not moving that f pawn? 

My point is that with this move, you will indeed cause some trouble to someone at my level (and I guess at your level too)... and you "call" for a refutation of your move that may not succeed  but may involve the Queen.

One of the biggest opening principles is to develop minor pieces, generally keep heavy pieces behind and flexible. 

The knight is more flexible than the bishop by nature, so bringing it out first is preferable. You can decide where to put your bishops after you have at least one knight out. Also the knight blocks the king from castling, so you're usually gonna have to move it anyway.

Your pawn strategy is often refutable: good development and pawn breaks smash open the position and the opponents development advantage becomes overwhelming.

I have carefully re-read the post and i have missed the point, it was more like a casual interest of the OP about most regular moves rather than some specific strategy discussion so my thread does not belong here actually, sorry.

Speaking related to the subj, while i encourage Neryssa's decision to play non-standart openings and i do that myself, Nf3 is just a default move and that knight will go there anyways in almost any case. I personally prefer to move pawn f pawn before that knight and put a knight behind it, but speaking of knights i play c3 one before that one. Knights are the things that do the frontline stuff while other pieces are more positional say sniping so you would want to keep knights active.
Hello from St.Petersburg though

Can anyone explain why in almost EVERY game that I play, my opponent will bring their knight into play on the 2nd or 3rd move. I NEVER play like that, I always open with the queens pawn up 2 and then make a diagonal line of pawns that protect each other, most of the time it confuses the opponent as they're expecting to play someone who also moves their knight 2nd or 3rd move, and therefore don't know what the hell to do. (I usually tend to quickly remove their initial knight with a knight/bishop exchange, which a lot of the time they take with a pawn and therefore create a double pawn line which is never a good position to be in).

Furthermore, continually moving a knight away from attacking pawns at the start of a game (because they've brought it out with no protection) is also never a good idea because it greatly increases the chance of the knight just being blundered.

So for the life of me I really can't understand why anyone would choose to bring knights into play so early in a game in every game.

You are playing like a beginner with beginner ideas.

Getting your pieces active is an advanced concept for players who are better than beginners. Your opponents are ambitious. They want to improve.

You are playing like a beginner with beginner ideas.

Getting your pieces active is an advanced concept for players who are better than beginners. Your opponents are ambitious. They want to improve.

'Beginner' and 'beginner ideas' are merely relative concepts.
I prefer to play outside the box, it makes it more interesting than just being a clone

You are correct that the terms are relative. By the standards of highly skilled chess players, I am a beginner, too. Nf3 is my usual second move as White.

If you care about playing well, don’t reinvent the wheel.*

Mikhail Tal used this metaphor in his introduction to The Last Check by Viktor Khenkin.

A castled king is always vulnerable after a pawn push. I enjoy mixing it up even more by castling on the queen's side, meaning that since most players castle on the king side, my pawns are already most of the way to breaking a castled king formation before the player has even castled. I've won numerous games within a couple of moves after an opponent has castled because they more or less castle into an instantly losing position (admittedly I play at lower levels, nevertheless, castling, imo, isn't always what it's cracked up to be and I often play (and win) without even bothering to castle myself.