When you play a piece, what sort of feeling are you trying to convey through the music?
A romantic piece is typically played with sentimentality and softness, made up of flowing measures and a light melody.
A celebratory piece is emphasized by its intensity and passion. The notes are short and loud and excited, lifting the spirits of those who hear them.
A sorrowful song is mournfully performed, sweetly and slowly progressed into a crescending waterfall of sound.
The rise and fall of the music enables a performer to create a story through his/her piece, drawing the listener in with proper enunciation and emotion. Dynamics and sensitivity to the mood of the composition are so, so important when attempting to convey the message that the composer of the piece wrote into the music. Expression is the number one tool to making a piece worth playing, and showing that it means something to you personally and you are performing it to the best of your ability.
Mistakes do not matter as much when the mood is the focal point of a performance. As long as you are in the moment, full of life, absorbed in the piece you are performing and showing the emotion you feel...
...the music will be beautiful.