The Greek word that is translated "repent" is a compound word meta-noya... meta = change noya= mind.
Real repentance is a change of mind, you must change what you believe before any change in behavior will be lasting!
Do believe you are a failure? Then you will eventually fail. Repent!
You are a new creation in Christ! The old you is passed away and now you have become new, a brand new you that did not exist before. The Greek word that is translated "creature/creation" in 2 Corinthians 5:17 KJV
(( Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new.))
That word in Greek actually means species... A new species of you!
Repent (change your mind) and believe!
Romans 10:10 KJV
 For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.
You can see here that the believing comes before the behavior... we believe and then we speak.
Change your belief first... Then your behavior will change!
This change will remain.
Repent from self righteousness and believe that you are righteous in Christ!
Your righteous standing has nothing to do with your behavior... Only your believing!
If you fail you are still righteous because it is not you! It is Jesus, it is Christ in you that makes you righteous.
It is important to believe in your imputed righteousness especially when you miss the mark! Because the righteousness of God is not about you and your performance or behavior.
(the word imputed means it was given to you as a gift, not a payment that you earned)
All you can do or need to do is believe and by believing you receive ! Repent!
Now that you understand what repent really means it doesn't sound so impossible anymore does it?
Once you really believe that you are what God made you... holy and blameless and righteous in his sight in Christ, then you will behave righteously without even trying, not because you are trying to become right, but because that is who you are... this new creature that you have become.
I think where many people get hung up over this imputed holiness that we have in Christ is that they don't understand what the word "holy" really means... it doesn't mean "perfect" it means "set apart to belong to God" there is a big difference! I am holy because I am set apart (from the unbelievers) to belong to God! that doesn't mean I am perfect it just means I am different, I am a believer! I not only believe in God but I believe God! I believe what He said!
It doesn't take faith to live by the law, it takes faith to live by grace!
I am not doing it, I am believing that God did it! And the finished work is being revealed in me more and more.
Focus on Christ in you! The hope of glory... the hope of everything!
The real gospel seems to be too simple for some people... and it is!
Baby trust Jesus! That is all!