Let's think of a song everybody knows.
Everybody knows "Happy Birthday To You". You know the melody to "Happy Birthday" better than you know the chorus riff to "Layla", the hammer-ons for "Eruption", the slinky lick for "Soul Man" — any piece of music you know, you know "Happy Birthday" better.
So try to play it.
All the way through.
It is hard. It is the reason for a lot of the stuff we do. We know scales because melodies, in general, come from scale notes. We learn the neck so, if we want a note, there it is.
Really, we make connections, learn positions, find licks, do all this so we can play stuff, but most of us, myself included, trap the music in our heads with our incomplete neck knowledge.
Which is why and how we suck.
I've been told that A-list players have been caught by this. Players whose day job is playing sessions. Players whose day job is playing instrumentals. Players whose day jobs are playing bluegrass instrumentals. (This is my bias: I consider bluegrass musicians the best popular music musicians out there. Not better than jazz musicians, although there is some overlap. Besides, jazz isn't popular music.)
If you come up with a melody line, a "skiddly be-bop", we should be able to play "skiddly be-bop". If we can't, we suck. By trying so, starting with "Happy Birthday", Patty and Mildred Hill's contribution to the arts, we can strive to not suck.
Do you have exercises or methods to help you not suck?