I am often asked the question, “Can he sue me for that?” or “Can I sue him?” and my answer is always the same: Yes. Anyone can sue anyone else for any reason. As long as the plaintiff (the one doing the suing) is willing to sign a Petition (the paper that initiates a lawsuit) and pay the filing fee, he can sue whoever he wants. Whether the lawsuit gains any traction is another story.
Believe it or not, people have sued God. In 2008 a Nebraska State senator sued God, but the lawsuit was dismissed because God could not be served with the Petition. Read about why the senator did it here.
On a more serious note, and specifically when potential clients ask me if they can sue someone else, my response is more that of a counselor than a lawyer. The Chicago community is a small one, as we all realize when we are always running into people we know in random places. The Chicago business community is even smaller. If there is a business relationship, one has to think about your reputation and the fact that word may get around if you are a lawsuit-happy business owner. For example, if a supplier has breached a contract, it is usually not the best idea to hire a lawyer and sue them right away. It is always a better idea to negotiate a new contract (with the aid of a competent business attorney) and keep the relationship intact. Lawsuits are expensive, extremely invasive due to expansive discovery that places details of your businesses in a public record, and they are bridge-burners. Suing should be a last resort, only embarked upon when negotiations have fallen apart. Sherman Alexie once said, “When you resort to violence to prove a point, you've just experienced a profound failure of imagination.” Similarly, when you resort to suing to prove a point, you've just experienced a profound failure of negotiation.
On the flip side, if you have been sued, you need to contact an attorney without delay. Even if you think that the lawsuit is frivolous, if you do not file an Answer with Exceptions (a response to the accusations along with reasons why the lawsuit should be immediately dismissed) the Plaintiff will get a default judgment against you within less than a month. Don't just think to yourself that the Plaintiff can't possibly get away with this – remember, anyone can sue anyone else for any reason.