Bass guitar player Phil Lesh as an example...
At age four, held his ear to his grandmother's radio and became enthralled with the New York Philharmonic playing Brahms’ First Symphony.
As a young kid, Lesh played the violin in Berkeley’s Young People’s Symphony Orchestra.
At age 14, he traded in his violin for a trumpet. Despite having only a year of trumpet behind him, he soon achieved first-chair position in a semi-pro Berkeley orchestra.
Throughout his teens and early adulthood, Lesh remained fascinated by the world of avant-garde classical and modern jazz, and was particularly intrigued by the sounds of Miles Davis and John Coltrane.
At the College of San Mateo, he became well-known for composing big band music, while continuing his position as first-chair trumpet.
He then took graduate courses in composition under avant-garde Italian composer Luciano Berio.
He lost interest in playing the trumpet and began to focus more on composing music.
He met Jerry Garcia, and Garcia asked Lesh to play bass guitar in his band, despite Lesh never even picking up a bass guitar before.
Lesh learned the bass in 2 weeks, and grew to arguably be the most inventive bass player ever.
Despite appearances, all of the band members, each with different influences, were serious musicians who weren't "playing around".
You be happy too! 
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