You can disinherit someone if you so choose. This means cutting someone out of your estate plan when they logically expected to receive something as your heir. Most of the time, this means leaving out one of your children. 

However, it’s important to note that a disinherited individual may have options to challenge your decision. This is a common reason for an estate dispute. 

For instance, they may say that you were unable to make that decision on your own due to your mental state or the fact that someone else used undue influence over you. They’re not claiming that the will or trust does not cut them out, but they’re questioning the validity of that decision and whether or not it really goes along with your wishes. 

Another issue could be if you simply leave the person out of the will, rather than writing into your will that you do not want to leave them anything. It may seem easiest to leave them out, but the issue here is that they could argue that it was just an oversight. They may claim that the will is incomplete. They may say that you just got confused and forgot to leave them anything. In this sense, saying nothing leaves the door open for a dispute, whereas listing them by name and making your intentions clear does not. 

Disinheriting someone is a fairly complex process and it can be controversial. Do not take it lightly. If it is something that you want to do, make sure you are well aware of the legal options that you have