Leviticus 4

“Speak to the children of Israel, saying: ‘If a person sins unintentionally against any of the commandments of the Lord in anythingwhich ought not to be done, and does any of them...‘Now if the whole congregation of Israel sins unintentionally, and the thing is hidden from the eyes of the assembly, and they have done something against any of the commandments of the Lord in anything which should not be done, and are guilty...‘When a ruler has sinned, and done something unintentionally...‘If anyone of the common people sins unintentionally." vv.2,13,22,27

Read chapter 4.
Can you sin without knowing?  Yes you can and in this chapter talks about the sin offering for unintentional sins.  We see that even if one did it in ignorance they were still guilty once it was brought to light.  There are more than just a handful of sins and definitely not an offering for every sin that there is or the work of the priests and the altar could never keep up, it seems that this sin offering was kind of a "blanket" offering.  This unintentional sin is not just by a single person but also for the whole congregation, rulers, common people.  We have to remember that even those we look to in leadership in Christianity error and also a whole community can follow a way of error and be at fault.  We should always take it to the Lord to know what His judgments are at setting things right.  When have you sinned unintentionally and realized your guilt afterwards and what did you do about it?  Luckily today we don't need to offer sacrifices for sins known or unknown because Christ has already paid that debt no matter the sin, but it is still good to ask the Lord for help in that area of sin.