I am a case in point.
When I was young, I was told I could not sing. I sang less and less as I got older. Each time I did, I was told to stop. More and more time passed between attempts.
When I got my first car, I sang loud and proud along with the songs I’d play on my cassette deck. My voice became strong and clear, but only when I was alone. As described above, I rarely sang for other people.
Finally, my senior year in high school, I decided I would audition for a musical play, taking advantage of my newfound confidence. I sang the first couple of lines very, very well, and I noticed the people watching were surprised, as I wasn’t supposed to be a singer. Then my subconscious caught up with me, reminded me I couldn’t sing, and the rest of the song went very, very badly.
I did not sing at all for the two years following high school.
Then I went to an arts college to pursue an acting degree. Everybody was required to take extensive vocal training, in tone, technique, and so on. And after a couple of weeks of instruction, I discovered that, by God, I really could sing after all – not just adequately, but very, very well.
Now, I consider myself an excellent singer. My range stretches from high baritone all the way up to almost the top of a classical tenor. I have excellent control not just of pitch but also of timbre and other qualities, including a vibrato that can be as aggressive as classical opera and as nonexistent as barbershop.
I achieved this because I (1) got over my insecurity and (2) learned and practiced the mechanics.
And, most likely, you can too. I’ve met maybe four or five people in my life who were legitimately tone-deaf. Everybody else has simply been anxious and untrained, and therefore self-destructs when asked to sing.
Just my own personal anecdotal evidence…