So recently I tried playing the chords for a song with a few friends. Even though I can keep up a consistent strumming pattern and change chords easily, I wasn't changing chords at the right time during the song. Apparently sometimes it was too slow, other times too fast--I can easily change chords even in the middle of a strumming pattern.

Someone I know has practiced for so many less hours for me and doesn't know any strumming patterns really, but can play just fine, whereas I wasn't able to.

So I'm really frustrated. Has anyone experienced this before?