I'm afraid my point was a victim of the 140 character limit. I don't think I was quite looking for the availability heuristic (which I'd already checked and discarded), but ended up tweaking my example to use it in the blog.
After you get a haircut you like, ask your stylist to describe what ey did/what the style is, ideally in the vocabulary of the trade. For instance, my current style includes a face frame, long layers, and some other style words.
Write it down, stick the note in your wallet, forget about it until the next haircut. You get the benefit of repeating instructions as they would be described from one hairstylist to another and are less likely to fall victim to terrible cuts or the poor memory of your regular stylist.
As someone who is less productive with a bad haircut (I have to pin unruly lengths out of my eyes, etc), this has saved me time and confusion.
I think I fall into the latter category, so here's my murky model and answers:
1) On two separate occasions, I recall explicitly turning down friends who wanted to create podcasts or writing projects. I was fairly sure I'd enjoy it, had expectations of high quality from the projects, and would have done it under different circumstances (being less busy). My initial feeling was fear of missing out--fear that it would be as fun as I anticipated, and that my reward would be "Well, I did have a chance to do that cool thing everyone else admires!" Later, it was more concern that I'd underestimated my ability to take on the responsibility. It was easier to decline because in both cases, they knew me personally, and I had more trust that they would believe me about being unable to take on more responsibility
2) I don't always use this model, and it could use improvement, but I weigh along stress and time invested. Time: how much practical time do I expect this to take, how well will that adapt to my schedule. (For instance, will it work with being totally unavailable during finals and midterms?) Time can obviously correlate with stress--something that eats into time to finish classes and other projects will inevitably cause stress. But stress also includes how much background noise the responsibility will cause in my life. Will I need to constantly be on the look out for podcast topics? Will I need to moderate comments continuously? Will I need to present myself differently on social media that has previously been simply, well, social? If I need to shift around other projects, will anticipating telling people that make me too anxious?
4) Yes, up until the last year or so. I changed from a series of events.
-Friends and classmates regularly remarked on how busy I was, which made me realize that they would be more open to me saying "No, too busy!"
-I started with practical training in my psychological services classes, which involves a lot of learning how to get other people to set their boundaries. It generalized.
-I started traveling more regularly, which meant having the easy excuse of being out of town, which meant getting more used to the idea that people took 'no' much more positively than I'd been imagining.