Never* say no to yourself. This has become another personal axiom, adopted from a good friend of mine who taught it to me. On the surface, it may seem selfish or arrogant, so let me explain exactly what it means, and just as importantly, what it doesn't. (See author's cautionary footnote.)
Have you ever desired something that required action by someone else but then assumed they would say no, so you didn't even ask? (ie: you'd like a raise, need a ride, or some other minor favor.) Instead by not asking, you essentially said no to yourself - probably out of fear of rejection or embarrassment, or a lack of confidence. If you think about it though, getting a 'no' leaves you no worse off than if you hadn't asked. The potential benefits of being surprised by a 'yes,' however, are enormous. I adopted the "Never Say No to Yourself" philosophy 100% after my friend convinced me to ask for something I was 100% convinced would be denied. Not only was I wrong, but they were delighted to accommodate my request. I was pleasantly stunned - and became an enthusiastic practitioner ever since. Of course, the answer sometimes comes back 'no' too. Don't sweat it. You're no worse off for having asked.
One last point - this axiom is not intended to be taken in a context of "do whatever you want" or "deny yourself nothing." There are numerous instances when saying no to yourself is absolutely required and appropriate. (You know exactly what I mean!)
I urge you to conquer your fear. There are plenty of people who will say no to you. Don't say it to yourself. Simply ask. See what happens. You might, like me, be pleasantly surprised at the results!
* Author's Note: Never does not mean Never. Apply axiom responsibly and as intended or suffer irreparable consequences of your own making.