Boredom. Yes having a child with autism is a lot of work and we have all heard it all before. But what no one will tell you is that it comes with a metric ton of boredom. Pushing the kiddo in a swing for 10 minutes = happy bonding time ... pushing him for 45 minutes = boring. Taking the same walk for the 800th time = boring. Spending all weekend, every weekend trying to get him through the day vice going out to festivals etc. boring.
I often hear that parents of children with autism have developed patience to bacon like levels of awesome. Most people think that comes from the direct interactions with your kid. I think it comes from learning to tolerate or find the good things in the boredom.