Commitment. ENFPs tend to move from one interest to another, often before significant mastery/accomplishment. I've played violin for 15 years and played in the orchestra all that time (up to this day). Yes, I've played a crap load of other instruments, but because of my fiddle, but I'm no "jack of all trades, master of none."
...Nevertheless, on a small scale (like with little tasks), I'm not as committed... I have a really hard time forcing myself to finish little things. I can come within a minute of finishing a level on some game, and just stop because I already know I can beat it... no more challenge.