“Yet”
As you simply notice your Gremlin, your Saboteur, the negative voice inside your head, think about responding by adding "yet" to the sentence.
You're not fast enough...yet.
Not smart enough...yet.
You will get there.
Stay positive and keep getting better.
The "yet" will turn into you realizing and saying, I am fast, I am smart, I am beautiful, I am positive, I am delightful to be around, I am a ray of sunshine on a cloudy day, I am enough.
Create your life.