Therefore, since we are surrounded by so great a cloud of witnesses, let us also lay aside every weight, and sin which clings so closely, and let us run with endurance the race that is set before us, looking to Jesus, the founder and perfecter of our faith, who for the joy that was set before him endured the cross, despising the shame, and is seated at the right hand of the throne of God.
Hebrews 12:1-2 (ESV)
How are you supposed to endure the challenges of the Christian life?
It is to fix your eyes on Jesus since He is the one who begins and completes your faith. Your faith is not about becoming a better Christian. It is to be Christ. As He is, so are you in the world (1 John 4:17). If you understand by revelation that you are a new creation created in true righteousness and holiness (Ephesians 4:24), then Christlikeness is not a goal, but a gift.
If you see Christlikeness as a goal, you will put more effort into achieving it rather than looking to Jesus and resting on what He has already done for you. You will become burdened by your constant failings or become blinded by your attempts. In any case, you will become self-absorbed and introspective, losing sight of who Christ calls you to be in Him.
If you see Christlikeness as a gift, then your focus is on being the person He has already created you to be rather than on what you should become. Abide in Christ and you will grow well in His grace and love. His Spirit who dwells within will produce the fruit or the character traits of God in you.
So, if we are not growing as much as we should be, it is not because there is something wrong with ourselves. Rather, there is something missing in our experience of Christ. For example, if anger is your default emotion, it is not because you lack love or kindness (since we have everything in Christ), but because we are resisting God's grace to be loving and kind (2 Timothy 2:24; Titus 3:2).
If you feel your spiritual experience is lacking anything, simply ask the Holy Spirit to reveal the truth of the gospel to you again and to help you in living in the reality of being in Christ.