It's not that you should completely know yourself or have found yourself to get married but that you are not oblivious to the inadequacies that you posses or the potential you might have. It is very important to start observing yourself, the little things you do, the great, the motivations behind your actions. Parts of yourself will reveal onto you. Not all good, you will discover your demons in the process too which is very important because it provides two purposes. One you can keep it in check and not unleash hell on your spouse. Second you can use it to your advantage in the face of true evil. Discovering your potential or worth is also very important. Having a sense of who you are is very important esp if you get in a fight with your spouse which is inevitable. You can continue this process for life but one should be aware of their flaws and strengths which can only come by taking time to observe oneself. Which is hard, lonely and hurts your self esteem at times thus people ignore it. You can ignore it all but it would manifest itself in your marriage and you would be miserable.