A video analyzing Symphonie Fantastique's 5th Movement, the latter half of which is in C major with moments of both its parallel and relative minors (C minor and A minor, respectively)

"Completely pure. Simplicity and naivety. The key of children. Free of burden, full of imagination. Powerful resolve. Earnestness. Can feel religious."

C major is, quite literally, the most simple scale one can get. With no sharps, no flats, and no special modifications, this key is extremely easy to play in, particulary for keyboard instruments, like the piano or marimba. On brass instruments, however, it should be noted that this key is notably difficult to play in, as the chord tones C (root) and G (5th) are notably out-of-tune on most of them, like trumpet and trombone. On these instruments, B♭ major is more commonly taught first due to its better intonation.