Immediately in the first ayas of the Baqara Sura it becomes clear who is certain, unshakable, firm in his/her faith. The one who has no doubt at all about:

This is the Book; in it is guidance sure, without doubt, to those who fear Allah. (Quran 2:2)

Who believe in the Unseen, are steadfast in prayer, and spend out of what We have provided for them; (Quran 2:3)

And who believe in the Revelation sent to thee, and sent before thy time, and (in their hearts) have the assurance of the Hereafter. (Quran 2:4)

Moses was also surrounded by skeptics:

We certainly gave the Book to Moses, but differences arose therein: had it not been that a word had gone forth before from thy Lord, the matter would have been decided between them, but they are in suspicious doubt concerning it. (Quran 11:110)

An example of the conjecture on which faith is based:

That they said (in boast), "We killed Christ Jesus the son of Mary, the Messenger of Allah.;- but they killed him not, nor crucified him, but so it was made to appear to them, and those who differ therein are full of doubts, with no (certain) knowledge, but only conjecture to follow, for of a surety they killed him not:- (Quran 4:157)

This leads to the following derivation:
Certainty is 100% commitment to a statement, to faith. In Arabic this is Yaqeen يقين
A commitment of around 70% is Zann ظن ,i.e. conjecture, not complete certainty.
The 50% commitment is doubt, concern, for which there are two words: Reib ريب and Shekk شك
The weakest attachment to a concept is called Wahm وهم ,which means imagination, hallucination.
Of course, the percentages are only to express magnitudes.
These are brain-sharpening concepts that are important to master in order to examine our own claims accordingly before making a statement.
When considering the opinions of others, and even analyzing the measures taken over us, it is good to clarify the strength of the concepts. You should know, that you choose your law, not the law chooses you. Provided you are conscious.