I spent years trying to learn how to improvise on the trumpet. It felt impossible. Every time I tried, it sounded really bad.
But when I first started taking comedic musical improv classes, I found vocal improvisation to be effortless. I'm not talking about lyrics, song structures, rhyming etc. I'm talking about improvising melodies and harmonies to the chords the band is playing. I don't have to think about it for a second. It just happens.
I wish I could do it with instruments too.