I don't care whether the world is a positive or negative place - I'm capable of having fun. That's positive thinking.
I often get so utterly intense - for a moment of time - about horribly negative stuff - so no, optimism definitely isn't simply about ignoring or denying reality but it can include being very intense about hellish circumstances and awful emotions - but if I didn't, I don't think I could be as intense about positive experiences.
What's going to happen is going to happen. Preparing is good - at least I think it's good to prepare if preparations or a lack of preparations will influence the outcome. Being autistic, I know lots of things are hard and I don't become non-autistic but I can prepare. And while preparations almost never make things "perfect" (unless we're talking about a perfect score on a test) they do create positives amidst the bad things.
Dwelling, being stuck on - as opposed to exploring the possibility in great depth to figure out out just how bad it was or will be - on great disasters and personal tragedies and how there is the possibility of a negative outcome to almost everything while ignoring all the amazing stuff there is all around us every day, all those little things - well, that's pessimistic, right?
Maybe some people don't care or they haven't yet stopped to think about it, but I don't want to miss out on anything so while I do think that negative thinking has it's time because negative experiences are perfectly real (and ignoring them can't be overly healthy), it's can't be a 24/7 occupation during which a vast amount of positives get ignored and rejected. Ignoring positives probably aren't the best way to making note of positives and to experiencing positive moments in life.
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Autism + ADHD
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The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it. Terry Pratchett