Harriet Schock is a successful Songwriter, Recording Artist, and Performer. On the USA Songwriting Competition blog she wrote that there’s a lot to say about “wrong notes.”
Some notes really aren’t wrong, but they are unexpected and give color to your music. Some occur from a grace note performed before a note of the melody and falling on the music beats (a.k.a. appoggiatura). Many songwriters and musicians have made a lot of these notes, and this can be a great thing, otherwise the melody is too diatonic (like only coloring inside the lines).
Click here for more information on how to use wrong notes to your advantage as you create music.