I believe 90-95% of my issues in life are because I can't speak up for myself

I find this happening more and more as I get older. I don't know if its just a natural part of aging that you just care less if someone is upset with you.

I've been there. Not a day goes by that I don't think about just taking a vow of silence and never speaking to anyone again. Maybe the monk life is the good life for me, who knows? I think frustration from confusing social interactions is my number 1 trigger for a meltdown and probably the thing that causes me the most despair about life as an autistic person. All we can do is our best though, and then try not to ruminate over it after :P 

There have definitely been times I've agreed with something on the spot and regretted it. Someone asked if I saw them as a friend, I said I wasn't sure and needed a bit more time to process it, and they said I was making them feel like they're not enough.

They were autistic too so it was probably inevitable that things would clash like that. I eventually caved in when I never truly felt comfortable and I do regret that.

I also went on a two-day trip with someone I went to school with - I was on friendly terms with him at the time but the whole thing was booked within an hour or two after first bringing it up. I would definitely not do such a thing now because although the trip went okay I just did not enjoy it at all. We haven't interacted since.

I could do something like "is it okay if I bring my contract end date forward to next Friday rather than two weeks later" when it came to work but it felt safe to do that because of the formal setting. Anything less formal is a nightmare.

That's true. I'm such a people pleaser though, it's little wonder that I find it so difficult.

I can sometimes say no, maybe to my parents if necessary, but outside of that there's no way unless it's a situation where it's very "open".

i.e. the other person has made it very clear that there's no pressure etc.

Once you learn that people can be unhappy with you and that's absolutely perfectly fine, it's quite liberating. Once you start testing the waters with it, it's even better!

Can absolutely relate to this. I never agree to anything on the spot if I can help if. Sit on it for ages sometimes then communicate the decision in writing where I can take the time to think about it and plan my words properly.

I'm like this with everything, my partner, work, buying stuff etc. Bought a bike from someone on eBay a few weeks ago. Went to have a look at it, thought it was overpriced, spotted it wasn't as it was designed (supposed to be a single speed but is a conversion, had a semi vertical forward drop out) one of the things I thought I'd filtered out when looking at the on the site, but STILL managed to agree to buying it.

Did the same with a car which I knew was going to be a load of problems, but in the moment ended up agreeing to take it.

Agreed to a holiday location that's going to be an absolute nightmare this year due to not wanting an argument about it with my partner. Last 20 years has been a nightmare of "going with the flow" into countless situations I don't want to have to deal with at all. Feels completely out of my hands which I think is one of the reasons I try to limit dealing with people directly.

My Gran, and most other women in my life, refused to take 'No' for an answer. One even yelled, "Do as I say!" to me; which I lied about when saying 'Yes'!

I need to learn, and grow, while they 'Don't want anything bad happening!'

I'm the same. It doesn't feel safe enough. 

Even though the absolute worst that could happen is that someone is a bit unhappy but I wish I didn't put that over my comfort. 

Same. If I said no, expressed unhappiness, or made the wrong facial expression as a child I would be threatened or hit. I still expect it to happen now.

Kickboxing, sword fighting and self defense classes have really helped me with this too :) It brings a lot of self confidence.

The pivot point for me was when the company I worked for sent me on an assertiveness training course.

It taught the theory then days of role playing to get it right - perfect masking training for an autist like me.

Now I can say no with confidence and not actually feel too bad about it - incredibly useful in my management career and when dealing with sales people - as well as in everyday life.

This is my problem too. I came from an abusive family where I was expected to meet the needs of a mother with very low self esteem and frequent volatile mood swings. I have found counselling to be helpful because most of the time I don't see a situation where I could be assertive until it has already passed, then I get all upset I didn't stand up for myself. I have found a good trick is to write down what happened in short form then add not what I should have done but what I will do next time. Then my brain kind of goes to that page if I'm ever in that situation and I can act on it.

Otherwise I have found it is a matter of delaying a decision. Don't agree to anything on the spot, be cagey! I have made a whole list of sentences that are along the lines of 'hmm let me check me diary'. 'I'll get back to you on that, I'm very busy at the moment', etc., anything to delay making a decision on the spot when I am most likely to blindly say yes. Delay, delay, delay and then take a moment when its quiet to go through a little list of the things people want from you and respond either yes or no in a calm fashion. With email being a common mode of communication now, it is a lot easier to say no this way later than say it to someone's face in the moment. Unfortunately I have learned this is something that comes with practice but it is something you can get better at :) 

I think it's definitely masking or something like that. I'm too concerned about offending the other person simply by saying no when I could probably put myself first more.

I've been able to do it in very small doses but not setting some kind of boundary has gotten me into dangerous situations.

I think masking and alexithymia play a big part that for a chunk of our lives we go along with things that everyone else does without realising we can say no.  Setting boundaries gets easier with practise,  people don't like it at first but they get used to it. Oftentimes I need time to process what it is I need or want. Burnout has taught me the importance of saying "no".

I think the easiest way to deal with that is reduce the fear of physical attack by desensitising your self to it. Maybe try some martial arts that encourage sparing, or try boxing maybe.