As a choir director, Music educator & private voice teacher & coach for many years, I have found many people had an event in their youth where they were put down openly by others, often a teacher or older sibling. Then there are those who need to be in the middle of strong singers.
Some folks just can sing melody only, and not harmony. I once had a small group of people from which to make a "choir." One guy could not find the bass notes to save his life. But, he was terrific & on the melody, so I made the 2 or 3 guys the melody singers, & the gals were singing alto & tenor to make a nice 3 pt harmony.
   Once a fellow came to me for private lessons at the suggestion of the folks who danced at the square dances which he called. He could not match pitch. Not at all! He was quite serious about learning to sing. I had him come twice a week for about a year, as we worked at finding pitches & learning intervals. He was eventually able to sing simple melodies similar to "Skip to my Lou," and other dance tunes as he called the dances.
   I wouldn't have put money on it before, but I learned that if the true desire is there, and an educator is willing to be flexible, anything is possible to those who believe.