This is a tough question to answer. While aiming to make your art exactly what you had envisioned is important, if you get too bogged down in perfectionism, you might not finish, or worse you might not end up making much at all because of fear.
What's the solution? Every artist looks at their work and sees nothing but the mistakes (so they say.) Perhaps we have to keep our eyes on our work and on the clock too. Set yourself a deadline for each piece and try to stick to it. When tackling those unfinished projects, have empathy for yourself but be filled with the drive to have fewer unfinished works, no matter what.
Let me know what you think of this question and how you've dealt with this issue in your creative life in the comments section.
Blessings,
--Pam