SINGERS! Is this you? :(
The vocal ligament (shown below) vibrates as AIR passes through creating a note or frequency. The ligament is like a rubber band. It thins for the high notes and thickens for the low notes, controlled by your brain called memory muscle. Just like the muscles and ligaments in your legs contract and relax so you can walk, also controlled by your brain. If your vocal ligament can contract/thin to the note you hear in your memory, then YOU CAN SING IT.
If you FAIL then you're simply not letting the AIR that is carrying the note, OUT. SO RELAX (especially the neck and throat muscles) and JUST DO IT! :)