If we would do that, we would have to block inside the actor, because all the operation we execute are asynchronous. The problem here is, that we don't know how long the operations will run and how long we should wait. Another problem is, that the user will not get any result until the other operation is completed and the requests may time out on the user side. I think it is better to let the user know that his operation can not be executed at the moment and let him retry later.