I think writers benefit from acknowledging their baggage and learning when it's useful and when it's detrimental and how to maximise the former and minimise the latter.
I tend to stick with what I know and have to push myself out of my comfort zone. When I'm writing I have to stop myself from trotting out the same situations/locations. Now I often leave out those details on the first draft so I can spend some time thinking up different set ups from my first reactions. When I'm teaching I often get the students to come up with words, or situations rather than coming with them pre-supplied. I'm always surprised at the range of what they suggest.
I was brought up with the idea that pushing yourself forward was bad. I don't like self-promotion, either doing it myself or hearing it from others. I vaguely hope that by being as good as you can be, somehow the magic universe will notice you. Don't get me wrong, I'm still a believer in self deprecation and not shoving oneself to the front, but I've also learned that the magic universe doesn't automatically notice you. You HAVE to get your work (and often, yourself) out there. If this doesn't come naturally to you, you need to find ways to get round it. I like chatting, so Twitter suits me, especially as overt self-promotion will lose followers. I don't like parties and schmoozing so I avoid those situations even though networking is good for careers.
Confidence, lack of. And the flip side of this is being overly impressed (and then depressed) by other people's achievements. Letting what other people achieve affect you is daft, but it's an easy trap to fall into. When I was doing my MA there was one person who became obsessed by other students' marks. It visibly corroded her belief in herself and her writing as she grumbled and complained about X getting a higher mark for their writing than she had done. I could suffer from this...instead I mentally stick my fingers in my ears and sing La La La when someone has just got some mega deal or sold shedloads in Tesco. It's irrational - just because X has succeeded doesn't mean I won't, so there's no reason to skulk back to my laptop thinking 'what's the point in carrying on?'
This post could go on and on and on, but I'd better stop for fear of boring you - which of course is yet another bit of my baggage...