Here are three of the most common misconceptions:
Firstly, nullity is said to be “Catholic divorce”: it is not. The Church recognizes that sometimes civil divorce is necessary when particularly grievous circumstances obtain in a marriage [e.g. severe domestic abuse] and, despite genuine efforts, cannot be overcome. Divorce of this kind has a counterpart in the Church's law in a process called "the separation of the spouses, with the bond of marriage remaining intact." This preserves the possibility, however remote, of future reconciliation before death. It also constitutes a powerful, if painful, witness to the nature of marriage and illustrates that a failed marriage is not always an invalid marriage.
But when divorce is understood to “put asunder” [Matthew 19:6; Mark 10:9] the bond of marriage, thus declaring someone free to marry again, the faith of the Church rejects this as contrary to the will of God [Genesis 2:24]. It is therefore also contrary to the true good of the divorcee who enters into another civil union whilst the bond of marriage to one's spouse is presumed to be valid. This is certainly a difficult teaching, but it cannot simply be ignored or contradicted by anyone who believes in God.
Sometimes, of course, situations evolve. A divorced person marries another; they have children together and so must assume responsibility for the children's upbringing and well-being. To do so is a moral obligation upon mother and father, as well as a loving service of care for the children. This cannot be denied. But neither can it be denied that this very situation has arisen as the result of a turning away from the original, and still existing, covenant of marriage with one's spouse in the eyes of God.
Divorce usually focuses on the circumstances around the end of a relationship. Nullity focuses more on the circumstances at the beginning of marriage while taking into account any indications of nullity which may pre-date or post-date the exchange of consent. Civil law grants a right to a divorce even when the grounds are not severe and even if the main reason for seeking it has only emerged very recently. But there is no right to a nullity. There is a right to petition one, but the decision of the Tribunal is not determined by the will of the party. It is determined by uncovering the truth at the time of marital consent.
Only if there is sufficient evidence of quality to provide the Judges with the certainty required by law to declare the marriage null does a person then have the right for the nullity to be declared - and the Judges have the duty so to declare it.
Secondly, in the nullity procedure no-one is personally on trial nor is it a rehearsal of divorce proceedings. The process is not about passing moral judgment on the parties to the marriage under investigation. It is not a “blame game.” What is on trial is the bond of marriage itself: was it, or was it not, valid on the day of the marriage? The investigation is therefore a technical and legal one. The language of the process is also technical. Sometimes it uses words which have a different everyday meaning, so it pays to be careful not to interpret some words too quickly.
It is only natural that one or both parties to the marriage may feel defensive, angry, bitter or even guilty. But the desire for or against a declaration of nullity is not decided upon feelings, no matter how intense, understandable or justified. The Judges will, because they must, take no side other than that of the evidence before them and their interpretation in the light of the law. Everyone is obliged sincerely to tell the truth, the whole truth and nothing but the truth. For this reason, an oath or a promise is administered to all parties and witnesses. An oath is an act of religion, calling God to vouchsafe for the truth of what the oath-taker is saying. Perjury in this context is not merely contempt of court but damages one's relationship with God.
It is also worth remembering that Judges are experienced people in terms of the law, of interpreting the facts and of spotting attempts to decoy or derail the Court from the truth. Judges do not want to be impressed. They want parties and witnesses to express the truth in answer to the questions put to them. It is this which leads to true justice.
Thirdly, the declaration of nullity refers to the bond of marriage, not to the entire relationship of the couple. Let us say that the bond of marriage is declared null. Let us say that no-one ever imagined that this was the case, but that the spouses lived in love and in commitment, with children and in untiring effort. Then, tragically, something fatal to the relationship appears [eg. extra-marital affairs; the death of a child; the onset of mental illness; etc.]. Does a declaration of nullity mean that all of that effort, love, parenting, sacrifice, etc., is also rendered null? Absolutely not. All that has been good and life-giving is not, and can never be, nullified by the stroke of a judge’s pen.
In addition, the Church acknowledges - in cases of a first marriage - the existence of the civil contract and its effects in the civil sphere and that the spouses were lawfully married in the eyes of the State. All children born of this civil contract are legitimate, including in the eyes of the Catholic Church. In keeping with her own law, the Church recognizes them as the legitimate children of a "putative marriage", i.e. of a marriage that was thought to be valid but, after due investigation, in fact was not.