Ever feel like you know what to say but can’t?

Ever feel like you know what to say but can’t? For me, my stutter only really happens when I talk to certain people. But when it does happen, it’s like I know what I want to say, how I want to say it, but it’s like somewhere in the process of going from my mouth to vocalizing the words, sometimes it’s like they get stuck almost. Like I just can’t get them out. But other times I speak perfectly fine. Especially by myself, I literally almost have no stutter talking to myself, but stutter on practically every 3rd word when talking to some people