Were you the kid in high school who proofed your essays before you handed them in? Or were you the kid who got the period in at the end of the concluding paragraph, and said, "I'm done with this!" and gave it to your teacher, whether it was filled with embarrassing typos or lines you accidentally wrote while watching TV and you inadvertently started typing what they were saying on the show.
Some of us spend days, months, even years preparing a script, a film, an acting portfolio, before we're ready to send them out to be seen by potential career-boosters (i.e. agents, studios.) I had a writing partner once who wrote draft, after draft, after draft of a screenplay, before ever sending it in. And I have been guilty of the "I don't want to look at this ever again!" team, and sent a script in to a VIP in the industry before it was really ready. The same goes for actors and other artists trying to get their work out there. Do you take a headshot and think, "Meh, that's good enough," or spend a year researching photographers to find the very best one?
Your screenplay needs to be right. Have others read it, or workshop it. Have a second set of eyes on your resume or your headshot. If you put out a crappy example of yourself, the best you'll get is a crappy agent.
As is with many things in life, the sweet spot is in the happy medium. Don't be so eager to get your script, headshot, resume, short film, etc., out there that you give them a mediocre product. You don't have a second chance to make that first impression. But at the same time, stop proofing and wasting time, and get that thing out there!
Find the happy medium: be prepared, but don't be late.