Looking at our stringed instruments, as well as the piano, they all start with the bass notes on the left side and move to the treble side, on the right.
Edit: What is the reason for that? Couldn't we just as well reverse them and put the treble on the left and the bass on the right? Is there a common reason for so many instruments going from left to right, or does each family have particular reasons?
Does this have something to do with the way we use our hands when we play?
Is it because western languages are read from left to right and the bass side is considered the starting point because it is lower in frequency? (I believe that oriental instruments also are set up the same way, although in that part of the world people do not usually read their languages from left to right.)
Edit: Perhaps a bit more difficult than those is the harmonica, which also goes left->right | bass -> treble, yet we only have one mouth. Besides, in our heads left and right are reversed. If you are right handed, you are 'left eyed' and 'left mouthed' (if there is such a thing): It is more difficult for right handed person to wink with their right eye than with their left. Things get reversed in the spinal cord.
Note: I'm leaving brass and woodwinds out of the discussion because there are often physical considerations that mandate they be constructed in a particular way: The treble end is on top at the narrow end, the bass end is at the bottom on wider end. But perhaps the layout of the valves and slides on such instruments is also relevant...