The more accurate way to put this is "I am not a Finisher". The argument here is that starting and finishing are two equally valuable skills that are somehow equivalent.
A "Starter" is a fairweather friend. It's easy to start things. Most people like starting things. Note this is different from networking and so forth, which is really a separate skill altogether.
Employers, business partners and investors will look at what you've finished and don't care what you've started. When something is 80% done or when times are tough or it's time to soldier on and run the last mile of the marathon, nobody wants the guy around who says "well, I started, that's my skill but I'm done now, I suggest you find a Finisher".
Not being a Finisher isn't a different skill--it's a character flaw.