Conscience is the "proximate norm of morality". Than means that it is the guiding light each person has to discern what is the moral value of any act. We have a duty to follow our conscience even if doing so means suffering or death.
However, conscience needs to be continually formed. The great sin of Adam and Eve was that they wanted to be the ultimate judges of right and wrong. They simply chose to live in darkness, away from the source of truth which is God. An essential article of our faith as Catholic is the belief that God gave the Holy Spirit to the Church making her the deposit of all truth in matter of faith and morals. Therefore we have an obligation to inform our conscience by:
Failing to do the above will expose us to the current of the world which will dull and weaken our conscience. A life of sin can deform a conscience and make it ineffective.