One of the most annoying types of people is a know-it-all, a person who has an opinion about everything. These are the type of people who is closed to anything new, resents discipline and refuses to learn. King Solomon calls these kind of people a fool. 

Pro 1:7 The fear of the Lord is the start of knowledge: but the foolish have no use for wisdom and teaching.

There are lots of people who may assume that they know everything. But we know for a fact that only God knows all things. Man was created with limitations. Even the brilliant people of their times admit that they cannot fathom everything in this life. Scientists fail on most of their experiments because of the unknown facts. The so-called missing link is until now missing and these so called brilliant minds are continuing to explore it. Some had died, others live to fail. Philosophers assume on things because they really don’t know the answers to some questions. Teachers and Professors, though their profession is to educate only know areas of their expertise and when asked about other areas, others might pretend but in reality, they don’t know what they are saying.

Pastors and Preachers who claim they read the Holy Scriptures for so many times, professed also that they know everything about God’s will and His commands, but some due to their lack of steadfastness failed. 2Pe 3:16-17  As also in all his epistles, speaking in them of these things; in which are some things hard to be understood, which they that are unlearned and unstable wrest, as they do also the other scriptures, unto their own destruction. Ye therefore, beloved, seeing ye know these things before, beware lest ye also, being led away with the error of the wicked, fall from your own steadfastness.

Indeed, there are some who claim to know they know everything, they know it all, but the truth is some of them are just pretending to be teachers of the law but their actions deny of the the true knowledge about God and His will. Tit 1:16  They profess that they know God; but in works they deny him, being abominable, and disobedient, and unto every good work reprobate. 

If people assume they know it all, they must be careful because the Holy Scriptures say that this is a form of foolishness. Foolishness in the Bible is in many forms and one of these forms is to assume that we know everything. It is foolish to assume the character of God being the only one who knows it all. Foolishness is a negative trait and it is being rebuke in many Scriptures.

A fool can do the following:

1. Can say that there is no God - Psa 14:1  The fool hath said in his heart, There is no God. They are corrupt, they have done abominable works, there is none that doeth good. There have been some, not many, who have denied the existence of God.  There are others who, without absolutely denying the Divine existence, deny his providence; that is, they acknowledge a Being of infinite power, etc., but give him nothing to do, and no world to govern. There are others, and they are very numerous, who, while they profess to acknowledge both, deny them in their heart, and live as if they were persuaded there was no God either to punish or reward.
2. Can blaspheme the name of the Lord - Psa 74:18 Remember this, that the enemy hath reproached, O LORD, and that the foolish people have blasphemed thy name. The heathen not only deny these things, but give the honor of them to their false gods, and thus blaspheme thy name.
3. Can foolishly insult God - Psa 74:22 Arise, O God! Fight for your own cause! Remember how godless fools insult you all day long.
4. Can despise wisdom and instructions - Pro 1:7 The fear of the Lord is the start of knowledge: but the foolish have no use for wisdom and teaching.
5. Assume they are doing the right thing - Pro 12:15 The way of a fool is right in his own eyes: but he that hearkeneth unto counsel is wise. What is it that keeps a fool from being wise? His ways are right in his own eyes; he thinks he is in the right in every thing he does, and therefore asks no advice, because he does not apprehend he needs it; he is confident he knows the way, and cannot miss it, and therefore never inquires the way. The rule he goes by is to do that which is right in his own eyes, to walk in the way of his heart. He makes his will his law. He is a fool that is governed by his eye, and not by his conscience.

God has no pleasure on fools and assuming that we know everything is an act of fool. We must be open to the advice of others, especially who know us well and can give valuable insight and counsel. We can learn things from other people too. Remember the saying, “we all need a mentor.”