We all have skills/habits that just take longer to learn.  Pullups, the habit of saving, heck just getting to the gym.  I have at times been embarassed by how long I have taken to become more consistent at double unders.  It has literally taken years.  Took almost a year to get the first one.  
Since that first double under it has been a journey that has taken years.  I have whipped myselft plenty of times.  I have lost them at times or at least had workouts that were slowed down considerably because I kept missing.  I have even gotten really frustrated during a workout, that was memorable and that very rarely happens for me.  I still  kept working at double unders though, not everyday.  Certainly at times weekly or at least a few times a week, and don't forget it has been years.  I have tried lots and lots of ropes.  I have combined double unders with other skills that I want to improve.  Recently I have jumped roped almost daily due to limited time for workouts.  I have coached others through the process and that has helped me tremendously.  Helping others helps you, more on that another time.    
I have gone from consistently inconsistent to understanding how to become more consistent at least for double unders longer and shorter duration workouts.  Double unders I tackled without a coach and I have also learned that I could have sped up the process with a good coach.  I also have more fuel to conquer myself.  I have gotten better at running.  I am able to jump rope daily (short periods) now for weeks at a time without knee pain and foot pain, as always technique matters(really matters footwork, hand position, core engagement).  I have sped up my goal to get 100 double unders in a minute.  I have broadened my horizons for fitness with a jump rope. 
See a challenge through especially the bigger challenges.  The harder lessons are the most lasting, memorable and most transformative.