I agree with ROWUK. I started playing trumpet in third grade (no lessons) - gave it up but took up piano lessons -- resumed trumpet in 5th grade (no lessons) - continued both piano and trumpet --- between sixth grade and junior high school (6 grade to 7) i had my first lessons -- took lessons in both piano and trumpet throughout junior high and first two years of high school. Then moved to a nearby city - no lessons. Bought an illegal "fake book" and took a few lessons on piano from a teacher who for the first time in my "education" introduced me to the circle of fifths. No more trumpet lessons for twenty years. Then, perhaps one year of lessons from the local symphonic principal. He introduced me to long tones and breath attacks.
Otherwise - it is the love of music and the drive to get better at what you do.