How can I have the success mentallity deep down in my system?

HAve you tried daily affirmations? I think that it would also be beneficial to write down all of the reasons why you want to achieve the specific goal that you are trying to achieve and to set short and long term goals. Reward yourself along the way. When self doubt creeps in, repeat your affirmations. One of my favorite sayings is "Fake it until you make it." Until you are successful, act like you are. If you persevere, you will achieve everything that you want to achieve.