Many people have second thoughts after they make a Will. Often they have made a Will years ago and just want to make one little change. They come up with their own solutions and the Courts see the same thing over and over again. Unfortunately, these solutions often have no legal effect.
Many people will often cross out something that they do not like in old Will and write in something new. They think that this changes the Will. However, in the eyes of the law, it makes no difference. When you originally get a Will, two people see you sign it and add their signatures as witnesses. This lets the court know that it was actually you who signed the Will. How is a court to know that you are the person who modified the Will by crossing something out and adding in something different? Because the court cannot be certain that someone else did not make the changes after you passed away, the court will disregard them.
There are proper ways to change a Will. You can get a new Will or you can get a Codicil that updates the old Will. Both need to executed with the proper legal formalities for them to be accepted in court.