Be the best of whatever you are.

We all dream of great deeds and high positions, away from the pettiness and humdrum of ordinary life.  Yet success is not occupying a lofty place or doing a conspicuous work; it is being the best that is in you. Rattling
around in too big a job is much worse than filling a small one to overflowing.  dream, aspire by all means; but do not ruin the life you must lead by dreaming pipe-dreams  of the one you would like to lead.  Make the most of what you have and are.  Perhaps your trivial, immediate task is your one sure way of proving your mettle.  Do the thing near at hand, and great things will come to your hand to be done.

If you can't be a pine on the to of the hill
Be a scrub in the valley - but be
The best little scrub by the side of the rill;
Be a bush if you can't be a tree.

If you can't be a bush be a bit of the grass,
And some highway some happier make;
If you can't be a muskie then just be a bass -
But the liveliest bass in the lake!

We can't all be captains, we've got to be crew,
There's something for all of us to here.
There's big work to do and there's lesser to do,
And the task we must do is the near.

If you can't be a highway then just be a trail,
If you can't be the sun be a star;
It isn't by size that you win or you fail -
Be the best of whatever you are!

The piece of paper, in my scrapbook, on which this is printed shows no indication of the author but through the miracle of the internet I now know that the above was written by Douglas Malloch (1877-1938), an American poet. 

[ muskie - a fairly rare North American fish of the Pike family ]