I’ve played and given up the mandolin several times over tge past several years. Longest continuous before now was maybe three months. What I’ve learned through my own learning process is:

1. Practice in time. Even if it’s slow.
2. Playing with backing tracks helps a ton
3. Posture is key. On my current streak of playing I was able to go from playing the melody of kids songs to the rhythm of some grateful dead songs (at 80 bpm instead of 140 bpm) after spending time watching videos of how to hold and sit. I then had to relearn all my fingerings but it didn’t take nearly as long this time.
4. Sucking is just part of learning anything new. I guess one either enjoys the act of improving independent of the current result or one doesn’t.

Post script: The reason I quit when I do is because I become frustrated with plateaus. I now believe a lot of these plateaus came from bad mechanics. My pinky could not reach the 7th fret no matter how much I practiced. I could not switch chords without destroying my rhythm or muting extra strings etc.