Most everyone has heard of the Seven Deadly Sins: Pride, Envy, Gluttony, Lust, Anger, Greed, and Sloth. I appropriated three from the original list and added some specifically for writers.
Pride - You have great ideas. You're creative, and you can write. Just don't take yourself too seriously and miss out on opportunities because you're unwilling to make editorial changes to your work. Everyone can improve, and all writers need beta readers, critique groups, editors, and proofreaders.
Envy - It's okay to be competitive. But don't get lost in "why not me" or "my stuff is as good as that author's." Concentrate on making your work the best it can be. Don't get stuck in an envy loop. Help others and celebrate their successes. Envy can bog you down and become a distraction to achieving your goals.
Over-commitment - Writers today have to be publicists, marketers, public speakers, bloggers, and social media strategists. Sometimes, life and work get in the way of writing. Strive for balance. And don't be afraid to say no to some of the requests that infringe on your writing time.
Distraction - If you yell, "Squirrel," my Jack Russell Terrier runs to the nearest window to locate the furry critter. I'm like that with the internet. It is way too easy to read email, check social media, watch a video or three, or research something. Again, it's all about balance.
Self-pity - Writing is hard work. There are very few talented souls who can bang out a perfect manuscript on the first attempt. Sending out queries to agents and publishers is also hard work, fraught with rejection. It's not uncommon for writers to get hundreds of rejections before they get to the "yes." Rejection stinks. Allow yourself a good sulk, but get back to your writing. Keep writing. Keep editing, and keep querying.
Sloth - I love snow days. When work is closed, it's my free day to read and write and do what I want. Just don't give yourself too many "snow" days. It is too easy to get distracted, and a short break turns into months and months. Don't journey too far from your writing routine.
Impulsiveness - I am as impatient as the next person. I love instant gratification, and I don't like to stand in line. But, make sure you're prepared when you talk to publishers, agents, and editors. Have your elevator speech ready. Make sure your query letter is polished. Unfortunately, you only have one shot sometimes. Don't burn them by not being prepared.
Best wishes with your writing. Enjoy what you do. It's hard work, and seeing it through to the end takes time, energy, and dedication.