This kind of thought process occurs for most actions or decisions I take. It's why despite mentioning my desire to start a webcomic three months ago I still haven't gotten around to it: I don't have confidence in the ideas I have; I doubt anyone will put up with my mediocre art despite knowing that the only way for my art to stop being mediocre is for me to draw something regularly - IE, a webcomic.
This kind of insecurity and lack of self-confidence is why I don't try to make many funny blog entries because I doubt my own humour. It's why I don't like to voice my own opinions. It's why I didn't kiss the girl that time - although that's a (hilarious for you, embarrassing for me) story for another blog entry.
But don't worry; miserable as I may sound I'm not wallowing in depression here. As a matter of fact I'm excited that Pokémon Black and White 2 is released soon!
I doubt I'll be any good at it though.