Basically, the answer is because regret sucks. To live life with a chorus of, "I could have's...." and "what if I'd's ...." running through your head is like allowing yourself to experience unnecessary bouts of weakness on a daily basis. To reach a goal is to have power over it. This doesn't necessarily mean you've executed it perfectly or that friends and neighbors applaud you for reaching the goal - maybe no one but you will even know what you've accomplished- but the point is that you've accomplished it.
"Do the thing and you will have the power. If you do not do the thing, you will not have the power." -Ralph Waldo Emerson
To pursue something that means a lot to you is to gain power. So, choose power and keep writing! That's one reason why I've decided to keep going with The South Louisiana High Book series. Is it great literature? Ha ha ha ha hahahahahahahaha. Um ...no. But is it fun to write and does it make me feel good to get these characters out there? YES! It gives me a feeling of muwhahaha!-like power. That's right, it makes me feel like a giant, which is nice because in real life I'm not all that tall. So, if you have an art project or a writing project that you're struggling with, I hope you find what it takes to finish it. Maybe that means asking for help or taking a few weeks break from it. Whatever the case, keep going!