How hard is too hard?

I'm composing a piano concerto with my basic knowledge of piano and based on what I've heard from other concertos... now, by all means, I can't play what I'm writing, but I've only just started learning piano. I do have quite an extensive background knowledge on music, but I'm just not sure what impossible actually is... does anyone have any advice or just general comments on this subject. I'm sure it'll not only help me, but many others here.

The best thing to do is bring your piece to a good pianist. Very often, when one doesn't know an instrument very well, things that are quite easy to play seem difficult, and vice versa.

That sounds like a really good idea. In my music department, there is an amazing pianist, so I'll see what he says about it... thanks for the tip!

I too sometimes compose something too difficult for me to play. But the important thing is you have the 'vision', all you have to do is find someone with the 'voice'. Good that you found someone.

The creed of the composer:

"If it's physically possible, and you can write it, someone can play it."

For example:
When Beethoven wrote his 5th Symphony, his orchestra complained that it was impossible. Now, youth orchestras play it.

Don't worry too much - simply go to an instrumentalist and have them take a look. (yeah, that was redundant, I know.)

For some practical theoretical advice I noticed that my hands span an 11th on the keyboard and not many have such a reach...So I found I put chords that were too big or too spaced out. It is a pitfall I fell into...Also just if you wonder if something can be done, try to think if you have heard something like that before. I like the find a pianist advice-it works!

That's kind of rare. 11ths can be played as rolls, though. I've done that many a time.

That is a good thing about having a basic understanding about the instruments you write for...which is why the only instruments I write for and don't know how to play is orchestral, and those are always for background

I can't play the majority of the music I write, but I know how it can be done and I've spent enough time listning to professional recordings and have heard what people who have mastered their craft can do. Your best bet (piano composition wise) is to sit down with your piece and see what kind of hand positions it requires to play your piece and if it is possible at speed. Listen to others and judge by their abilities whether or not something is entirely "impossible" or if it's just an enjoyable challenge.