When you hear a song, you hear all the component parts together, the drums, bass, guitars vocals, keyboards, horns, special effects if any, etc.
When you hear a single instrument out of context, it has a different appeal, and is often strikingly different than it sounds settled inside the “mix” of the final song.
The slide guitar work by Duane Allman for the classic Eric Clapton hit “Layla” is a great example of the very different sound one hears when comparing the individual instrument track to the song, fully mixed.
“Layla” is a song written by Eric Clapton and Jim Gordon, originally released by their blues rock band Derek and the Dominos, as the thirteenth track from their album Layla and Other Assorted Love Songs (November 1970). It is considered one of rock music’s definitive love songs, featuring an unmistakable guitar figure played by Eric Clapton and Duane Allman, and a piano coda that comprises the second half of the song. Its famously contrasting movements were composed separately by Clapton and Gordon.” – source
This video is Duane Allman’s slide guitar pulled out, separate from the full mix:
Now compare it to the full song, and you’ll see what an amazing difference you achieve in the full-mix.
This contrast may help you understand and even “feel” the importance of the role of mixing the recording so that all parts meld into a pleasant recording.