According to MN 9 (below), as long as you still have fermentation or effluents, you would still have ignorance, and vice versa. Ignorance is very a deeply ingrained and deeply lingering fetter. You know the Four Noble Truths, but when someone threatens your life, you may get scared. So, do you really know the Four Noble Truths in such a way that it dispelled your ignorance?
From the origination of fermentation comes the origination of ignorance. From the cessation of fermentation comes the cessation of ignorance. .....
From the origination of ignorance comes the origination of fermentation. From the cessation of ignorance comes the cessation of fermentation.
According to SN 35.153 (below), understanding by faith, by personal preference, by oral tradition, by reasoned reflection and by acceptance of a view after pondering it, is insufficient. It must be understood by "seeing it with wisdom". Only then does it dispel ignorance.
“There is a method of exposition by means of which a bhikkhu—apart from faith … apart from acceptance of a view after pondering it—can declare final knowledge thus: ‘Destroyed is birth … there is no more for this state of being.’ And what is that method of exposition? Here, bhikkhus, having seen a form with the eye (and same applies to sound and ear), if there is lust, hatred, or delusion internally, a bhikkhu understands: ‘There is lust, hatred, or delusion internally’; or, if there is no lust, hatred, or delusion internally, he understands: ‘There is no lust, hatred, or delusion internally.’ Since this is so, are these things to be understood by faith, or by personal preference, or by oral tradition, or by reasoned reflection, or by acceptance of a view after pondering it?”
“No, venerable sir.”
“Aren’t these things to be understood by seeing them with wisdom?”
“Yes, venerable sir.”
So, how does one "see it with wisdom"?
The answer comes in SN 22.98 (below), where Ven. Khemaka briefly describes the technique of Vipassana, as the method to be used to see with wisdom, in order to dispel the deep fetters of conceit and ignorance.
"In the same way, friends, even though a noble disciple has abandoned the five lower fetters, he still has with regard to the five clinging-aggregates a lingering residual 'I am' conceit, an 'I am' desire, an 'I am' obsession. But at a later time he keeps focusing on the phenomena of arising & passing away with regard to the five clinging-aggregates: 'Such is form, such its origin, such its disappearance. Such is feeling... Such is perception... Such are fabrications... Such is consciousness, such its origin, such its disappearance.' As he keeps focusing on the arising & passing away of these five clinging-aggregates, the lingering residual 'I am' conceit, 'I am' desire, 'I am' obsession is fully obliterated."