One of the fundamental pillars of being someone who executes (does executioner sound too extreme?) is trusting yourself completely. Only when you have that trust can you reliably reach goals over the mid and long terms.
By trusting yourself completely, I mean that if you decide internally that you are going to do something, you will almost certainly make it happen, and if it doesn't, the excuse will be really good.
For example, I decided 112 days ago that I was going to do a language tape every day until I ran through every Pimsleur method series for all of the major languages. Because I trust myself, I knew without any doubt that I would follow through and do the tapes. I did miss one day, because I got food poisoning, passed out, and smashed my face on the toilet. Even then I didn't mean to skip the tape, but I was so dizzy that I took a nap that ended up lasting until the next day. I accepted that excuse.
A good way to put "complete self trust" into context, is to think of how you relate with a trustworthy person. For example, I trust my friend and cofounder, Todd, completely. If he says he's going to do something, I have no tangible doubt that it will get done. If he's responsible for something, he will follow through.