Tristram is unusual in not needing a great amount of structure to his day as many people with autism prefer, but this doesn't mean we can just make changes in his life without a great deal of prior warning. He is generally quite easygoing and takes change in his stride once we have explained what is happening. Having said that once we have explained something that will happen - or has happened - Tristram will repeatedly ask questions and demonstrates that he is either confused or anxious.
We have to be quite patient and keep explaining, in different ways, if necessary, any changes or plans.
The first memorable occasion when we did not prepare Tristram sufficiently was when we had friends stay with us from the Isle of Lewis where we had lived for a time. Tristram was about 8 at the time and was delighted to have friends staying. They read stories to him, he enjoyed the shared meals and though quiet, he clearly enjoyed them staying with us.
However, they had to leave on a Monday morning when Tristram was at school. They made a big thing of saying their goodbyes to Tristram before he was collected for school in his special taxi and told Tris that they would be catching the ferry home that day. We thought Tristram had understood. He hadn't.
For the next few years (yes, years...) Tristram came home from school or sometimes out of nowhere he would blurt out "Where's my Daisy, Deb's and Dave?!!" He was clearly distressed and anxious each time and it obviously played on his mind. Because of this we now have to make sure that Tristram is around when people (or animals) leave. When his brothers visit we have to keep him off school, or even get him up if they have to leave very early, so he can say proper goodbyes, see them go and basically make sure he has real closure and a chance to do some 'grave dressing' by talking about their trip, them leaving and when we'll see them again. Even when a pet dies we have to be completely honest and allow him to see the dead pet. They do not 'go to sleep' or 'pass away'. They die. They are dead. We have to be brutally honest or he will think that that can awaken or come back otherwise.
We sometimes have litters of puppies that we breed specially as companions for families who have children with special needs who want a 'friend' in their lives but want to avoid the early puppy stage. The thing is they are going to leave at some point but Tristram has to make sure he sees them to say his farewells and see them go. It has got a bit easier as he has got older but we cannot just tell him a puppy has been sold and has gone to a nice home. He has to meet the people taking the puppy and give his 'permission' for the puppy to go to his/her new family. Tristram does a lot to help care for them when they are young so it is reasonable that he is part of the process anyway.
But all it really takes is a bit of careful planning and thinking ahead to avoid him getting too upset.
We still sometimes get the "Where's my Daisy, Debs and Dave?!!" though - I think that will always be there when he is feeling upset or anxious, sadly...