What's a relatively minor thing to most people that you WISH you could have?

Practice. A lot.

In my teens I wasn't able to carry a tune at all. Our music teacher marked me as "hopeless" after hearing a me singing a few lines.

This pissed me off royally. I had no desire or illusions of becoming a great singer, but I would not accept being "hopeless". So I started practicing with simple children's song melodies and recorded my singing with an old cassette recorder. It was indeed pretty awful at first, but I slowly got better. Then I got my driver's license and could sing along the songs from the radio and my cassettes while driving alone, it was a big step up from singing quietly in my room.

I also started playing the guitar to get a better understanding of musical theory, which was helpful. After I had learned the basics of playing rhythm guitar firmly I learned to play the piano. I believe that singing the melodies while playing them on the piano was essential to my development, since I could instantly hear if I did not hit the correct note.

By my mid-twenties I could already carry tunes easily and even got a complements about my singing voice. Key changes and modulations were still pretty challenging, but I kept on practising whenever I found the time.

Now in my forties I can repeat a melody correctly after hearing it once or twice and I consider myself a decent singer. I don't sing karaoke or any solo performances, but I do love singing backup or as part of a group.

If my music teacher hadn't embarrassed me publicly all those years ago, I most likely would have never put any effort in getting better at singing or learning to play instruments. I started this lifelong project purely out of spite, but it became a major and very dear part of my life. I even owe my marriage to music, while we were still dating my wife confessed to me that she most likely wouldn't have even noticed me if I hadn't been playing the guitar at that one summer party. Thankfully I wasn't too hammered at that time ;)