Sometimes we learn thing without realizing we have learned them. Traditions, values, even what we think is in the Bible is often unconsciously learned. At times, these things learned/not learned are good, sometimes they are bad. Regardless, they are deep within our DNA, like yeast baked into bread. We cannot see the yeast specifically, but we see the effect.
“Be careful,” Jesus said to them. “Be on your guard against the yeast of the Pharisees and Sadducees.”