I have believed something to be true when it is not true.
What is wrong with what you or I believe? What is wrong with the extent to which we believe? Do we really need to believe in anything?
There is nothing wrong with not believing in anything if there is nothing true that would benefit you or others of your life. If however there is something that is true that would in turn benefit you and others of your life, your wrong/ weak beliefs could have a very large cost.
Definition of a strong belief: A strong belief is a belief that you would die for.
They trusted in Him and defied the king's command and were willing to give up their lives rather than serve or worship any god except their own God.
How do you get a strong belief that is true? You need to receive an understanding of the truth from He Who is Truth. If He is not willing or able to give this understanding to you there is no point in your life.
Titus 1: 9
He must hold firmly to the trustworthy message as it has been taught, so that he can encourage others by sound doctrine and refute those who oppose it.
Buy the truth and do not sell it-- wisdom, instruction and insight as well.
The beginning of wisdom is this: Get wisdom. Though it cost all you have, get understanding.
In the fear of the LORD is strong confidence: and his children shall have a place of refuge
One who is wise can go up against the city of the mighty and pull down the stronghold in which they trust.
Wisdom makes one wise person more powerful than ten rulers in a city.