Think Soberly
Rom 12:3
For I say, through the grace given to me, to everyone who is among you, not to think of himself more highly than he ought to think, but to think soberly, as God has dealt to each one a (the) measure of faith.

When it says to not think of himself more highly than we ought, we must be aware that in the original language, the word "himself"is in itallics and is not there but was added by the translators to convey what they believed to true. The words "think highly" comes from the Greek, hyperphroneō which forms from two words hyper, which alone is translated; for, of, above and even abundantly or exceedingly, and phroneō which is translated; think, learn, minded. The root of this word phroneō is phrēn which is translated understanding but has reference to judgement or even heart.

Understanding this word becomes important as we look at the next part of this verse. We should think of ourselves soberly. Soberly is the Greek word; sōphroneō which is again from two words. It is clear that the second word is phroneō, but the revelation what the first part of this word is. it is the word; sōzō where we get saved, and know that it also refers to rescue, deliverance, healing, prosperity, and healing.

Really what Paul is saying here is to not over think about yourself, your problems, your issues, but to sozo think about yourself. Think of yourself as delivered, rescued, healed, prospered, and made whole, with nothing lacking and nothing broken. This why he goes right into the measure of faith, because thinking of yourself as sozo if the result of faith.

Paul began this verse talking about grace. The way the punctuation is inserted in to the text and the way they translate it, its as if Paul is speaking by a grace that was given to him words that were for all that are among them. But when I look at the interlinear, it appears more likely to me that he was declaring that grace was given to everyone among them. Which makes more sense as we discover the meaning of soberly as meaning to be understanding that we are sōzō (saved) . And then realize that the end of this verse deals with each being given the measure of faith. Suddenly we see a parallel between what Paul wrote to the Ephesians in chapter, verse 8. "For by grace you have been saved through faith, and that not of yourselves; it is the gift of God,"

Mar 5:15
Then they came to Jesus, and saw the one who had been demon-possessed and had the legion, sitting and clothed and in his right mind. And they were afraid.
Luke 8:35
Then they went out to see what had happened, and came to Jesus, and found the man from whom the demons had departed, sitting at the feet of Jesus, clothed and in his right mind. And they were afraid.

Sōzō thinking will cause fear in the religious.
Your thinking challenges their limited religious traditions.

Rom 12:3
For I say, through the grace given to me, to everyone who is among you, not to think of himself more highly than he ought to think, but to think soberly, as God has dealt to each one a measure of faith.
2Co 5:13
For if we are beside ourselves, it is for God; or if we are of sound mind, it is for you.
Tit 2:6
Likewise, exhort the young men to be sober-minded,
1Pe 4:7
But the end of all things is at hand; therefore be serious and watchful in your prayers.

Does your heart condemn you? 
1John 3:20, 21

20For if our heart condemn us, God is greater than our heart, and knoweth all things.

21Beloved, if our heart condemn us not, then have we confidence toward God.

At first look, it appears that these verses balance on the word condemns. This can be troubling because Romans 8:1 clearly says that there is "no condemnation" and now it appears that our heart will condemn us. So, at closer look, we find that this word 'condemn' is translated from the Greek word kataginōskō which is a combination of the two words kä-tä' which is a preposition that is translated many ways, but most commonly as according to, and ginōskō, which is to come to the knowledge of or learn. But has reference to an intimate knowledge, as in a man "knowing" a woman.
kataginōskō is only used in scripture 3 times and is also translated as blame, but I don't agree with the translation condemn as I understand the word. Because we know that there is therefore no condemnation for those who are in Christ.
That word used in Romans 8:1 is not the same word as above but is katakrima. It shares the same prefix Kata, but that is the only similarity to kataginosko. The second root word for condemnation in Romans 8:1 is krinō and most is often translated to judge.
Translating these words so similarly is like saying  two words that both begin with the prefix "pre" are the same in meaning. Such as prejudice and premonition. Completely different meanings.
So understanding that my heart doesn't condemn me, brings us to ask what this verse means.
Paul says that our hearts have been circumcised. Why circumcised? What is the significance of this. I have another teaching on the heart of a new covenant believer, but let me summarize with this.
When we are born again, our hearts are circumcised, which means the flesh is cut away, because the Spirit and the flesh can't reside together. Our hearts become the meeting place of our spirit and soul. The conference room, if you will. My heart is where the Holy Spirit speaks the truth of my spirit. It where all truth is revealed to me. My heart isn't wicked. It isn't flawed. It's not my heart that needs change, it's my soul, my mind, will and emotionsy that needs change. The renewing of my mind is how I'm transformed, not my heart. My heart is good and pure and communes with my spirit.
When you hear something that bears witness with the truth of your spirit, you know it in your heart.