The Power of No

I really need to learn the word "No."

"Brian, can you do this for me before the end of the week."

"We're booked solid for 2.5 weeks, but I'll figure out a way."

"Brian, can you write me a script? I don't have any details, but it's about furniture. I need a :30 and a :15.""

Sure, I'll have it by the end of the day."

"Brian, I need to take this :30, and turn it into a :10, but they want it to say everything it does in the :30, only shorter."

"Who gives a crap if it looks bad? I'll hack and slash."

"Brian, I see your schedule is full, but can I get you to edit something for a client? We don't have any elements, and they want it by tomorrow."

"Script? Who needs one? I'll just continue to pull crap out of my ass."

It's two letters, one word. "No." It's easily one of the most simple words in the language. Why can't I use it?