The necessity for tests

When you work on a project, chances are that you are not the only developer who will work with this code. Even in the case where you are the only one who will ever change it, if you do this a few weeks after creating it, you will probably not remember all the places that this piece of code is affected. Okay, let's assume that you are the only developer and your memory is beyond limits; would you be able to verify that a change on a frequently used object, such as a request, will always work as expected? More importantly, would you like to do it every single time you make a tiny change?