Definition of reality by Philip K. Dick

In the speech "How to Build a Universe That Doesn't Fall Apart Two Days Later" attributed to Phillip K. Dick (1978), he explains the motives that drove him to write, and a number of always current affairs:

It was always my hope, in writing novels and stories which asked the question "What is reality?", to someday get an answer. This was the hope of most of my readers, too. Years passed. I wrote over thirty novels and over a hundred stories, and still I could not figure out what was real. One day a girl college student in Canada asked me to define reality for her, for a paper she was writing for her philosophy class. She wanted a one-sentence answer. I thought about it and finally said, "Reality is that which, when you stop believing in it, doesn't go away." That's all I could come up with. That was back in 1972. Since then I haven't been able to define reality any more lucidly.