First of all, please do not consider everything you find here to be etched in stone. It is simply an analysis about various possibilities and situations. You should not start downloading a resignation letter template without reading a few advices.
Various symptoms emerge when people plan to quit. Some people become depressed, while some people simply switch to berserk mode. The worst case scenario is a complete mental collapse. It can burn out the person and destroy friendships and families. This sounds extreme, but it could happen. Fortunately for you, you can do better because you are here on this website.