In the English language, Catholics will often talk about the idea of falling into sin. At face value this could appear to mean that somehow we end-up in sin, without us even realizing what took place.
It's as if we fell into a hole of sin, not looking where we were going.
To a certain degree, there can be some truth to that statement. We can be led into sin unexpectedly through our actions.
For example, maybe we saw a scandalous ad when surfing the internet, and accidentally clicked on it. Initially we would not be at fault if we clicked on it by accident. However, if we choose to stay there and interact with the content of the website, then we would be committing a sin.
The Catechism of the Catholic Church explains how at the root of every serious sin is a free choice.
On the other hand, unintentional ignorance can remove our culpability, especially if it was a true and accident, and not something that we desired to commit in any way.
God inscribed the moral order into our heart, so even if we don't know all the laws of the Church or even the Ten Commandments, we can still have an innate sense of what is good or evil.
It is up to our conscience at the time of the sin to know if what we committed was a free choice, or if it was unintentional ignorance.
Falling into sin may be possible, but if we truly do sin against God, our action has to be free and not something that we do by accident. We need to take responsibility for our actions and if we are in a habit of sin, we need to break free from that addiction and experience the beautiful mercy of God.