This is a matter of principle...
If you start something, you commit to it and finish.
Firstly, you become selective about what you start, making you focus on what's important and/or influential.
When you do start, you also push through those days where you feel disheartened or want to quit. A feeling I often had when writing my book...
In the two years it took to write and self-publish the book, countless times I wanted to quit... "Is this really worth it?", "Why am I doing this?", and sometimes the sheer principle of finishing what I started pulled me through.
If you are a perfectionist, it forces you to either drop your standard slightly to push a project out and keep the train rolling, or you make it "perfect" - in my case, the book finally reached a state of what I deemed perfect.
Given that you are now investing your time and energy into what's important to you, the sense of fulfillment when you do push through and finish the job is unmatched.
This comes with a limit.
You have to be self-aware enough to know when to cut the rope and call it quits if something is no longer serving you.
For example, what is now @live.plans was previously @vagusnutrition - which I wanted to turn into a supplement company (and was pretty vocal about it).
Here the difference is in the intent.
Are you quitting, or are you cutting ties for something greater?