People with autism can be very single-minded. They can appear very stubborn and inflexible. A large part of this is because they dislike change. They often get deeply focused on one or two key interests, and these interests can be maintained well into adulthood. Often if someone with autism likes something they don't stop liking that thing. Most other people 'grow out of' interests and change tastes as they grow up. Those with autism frequently like the same music long after others have moved on to something else, they may play the same songs over and over again, they will like the same programmes and may watch those programmes repeatedly. As a teen I used to draw a felt tip line on video and audio cassette tapes to mark out where songs or programmes were. I would then watch the same TV programmes over and over again - for me personally it was usually documentaries about sharks or dolphins or whales, or Elvis Presley's 1968 Comeback Special, and listen to the same song over and over again - when I got a reversible cassette player I used to have Bohemian Rhapsody playing on both sides so that as soon as the song ended I could flick a switch and it would play the song on the other side of the cassette.
I'm now nearly 40 and I still like a lot of the same cartoon's I've always liked, I still like a lot of the same books I've always liked, and still like a lot of the same songs. I have added additional things I like to my list over the years, but I haven't 'grown out of' things I used to like. I have been obsessed with hypnosis and related topics, nature, and martial arts since being a child. I have always asked for exactly the same hair cut since being a young child until now (although I also hate getting my hair cut!), I will wear the same items of clothing day after day, year after year. When I like something I instantly obsess about it and have to know or have everything about it. So I like Katie Melua and have every album and released single by Katie, and can't imagine a time in the future where I stop liking Katie. I like Russel Watson, and the same applies, and Meatloaf, and The Piano Guys, and Jools Holland, and Elvis Presley. I like Derren Brown and have seen all of his shows (some more than once), and own all his books and DVD's etc, I like Hypnosis, so have everything by Paul McKenna (because of the impact he has had on my life), everything by Stephen Brooks, everything I can by Milton Erickson, and by Ernest Rossi, and Richard Bandler. I never really read fiction before meeting my wife, but she introduced me to Dean Koontz books, so I have almost all books by Dean, including many of his books under pen names, and I'm obsessed with wanting to learn knowledge - especially scientific knowledge, so have many science books.
Interests can often be a good coping mechanism to handle sensory overload and anxieties, you can become absorbed in the interest and so shut out everything else. Interests can also become obsessive because of having black and white thinking, often with people with autism things are all-or-nothing, so it is common to either not find something at all interesting, or be obsessed with the subject. This goes for other areas for the autistic person, they may either want something, or definitely not want it, or like a food or totally dislike it.
Usually the autistic person can be so interested in a topic that they are an expert in that one topic. They may have deficits in other areas of their life, like struggling with social skills, but may be incredibly knowledgeable about their chosen topic. Some will know movie lines by heart, or be able to recite dates and historical events. Some (though not as many as I think the public thinks) have a talent which stands above the talent of most other people, and yet may struggle hugely in other areas of their life, they could have a savant ability.
Those with autism also often want clear routines, this reduces uncertainty and helps to keep anxiety lower. I know I struggled as a manager, and one struggle I have self-employed is uncertainty and having to make decisions, I struggle to make decisions unless it is an emergency so that there is a clear over-riding focus which is on safety, so I am making a certain decision around safety. If I have to decide on less important things I struggle to make a decision and I want someone else to tell me what to do. I prefer being an employee who works a regular and unchanging shift pattern, where I do the same thing everyday, and if I had the choice this is what I would do. The difficulty is that employers add in tasks at short notice I'm not prepared for doing and I am uncomfortable to do, and many companies have a focus on trying to drive staff for progression within the company - again something I'm not comfortable with. Ideally I would love to be able to not work at all and just follow my interests every day, where I could go for woodland walks regularly, where I could study science topics daily, and focus all of my time on learning. Self-employed has a lot of jobs I struggle to do as someone with autism, and being a manager has too much focus on me being the one who has to make decisions. I can see why those with high-functioning autism who could work struggle to work. I work self-employed, and am much happier doing this than I was being in employment, but it is frequently very difficult not to quit what I'm doing because of all of the uncertainty and anxiety employment and self-employment can cause.
I find I can obsess about something or have a routine, that can change in an instant if things change. So when I did a road running race as a teenager I was nearing the finish line when a marshal told me the route had changed and I had to take a slightly different route to the finish line. My motivation to keep going faded instantly and although I was near the front I walked the rest. When changes in jobs I've done have happened I've quit the jobs rather than sticking with the changed routine. When I started a Master's degree, it was the most important thing I had done in my life (other than getting married) and within months I quit because of goal posts changing. As it was so important I tried fighting this, but couldn't overcome my in-built response to quit. This, and my black-and-white thinking are two things I would love to change about myself.