Note: if I say something problematic please mention it because I'm talking about some things I don't have personal experience with (chronic pain/fatigue/anxiety) so I may be off-base and have no idea.
Being late, cancelling plans, not being up for some activity; these things are called rude and that's fucking ableist. Why? because when people with chronic pain/fatigue/depression/anxiety/other disability can't make it on time or at all, that is not* because they don't care or aren't invested in you or don't respect you, it's because it would cause them damage to do it. When you value your own time so much that you would rather someone else be damaged than 'waste' your time, you are being incredibly selfish.
I get being an ignorant ableist poopsicle because I was one before I dated Kylei and before my ADD got unmanageably bad. Kylei deals with chronic pain/anxiety/ADD and often depression/insomnia-induced fatigue. I know how very much Kylei values time with people - it's way more than me, most of the time. Kylei would rather take damage than 'waste' someone's time and so when Kylei cancels, it's because it would really damage them. And yet I've known people who act like Kylei is proving they don't care when they are an hour late or cancel five minutes before or forget the plan entirely or get hyperfocused on something/someone else and don't check in for months. It's not fucking true and it's downright cruel to suggest that Kylei's core value is meaningless to them! (I'm not saying it doesn't hurt -- I usually am fine the first two times but when it happens more than that in a row I need some reassurance that they still care and want to spend time with me. I know logically that it isn't about me but I sometimes need emotional reassurance. Kylei is always quick to give that and quick to try any potential solution I come up with.) So yeah, seeing how much Kylei cares made me realize that (shock) being there is NOT a proof of caring. A bit after realizing that I began self-educating about disability and paying closer attention and I realized how much this happens. So many friendships are built on something that only non-disabled people are capable of doing. And the reason is that people give a completely false meaning to it. Someone can always keep their plans and never be late and always be up for doing the thing you want to do and still be a terrible friend.
So my basic, decent-human level of inclusion is to be prepared for something to interfere with plans, and not to take it personally. I communicate what I want (that you keep plans and let me know as far in advance as possible if you are cancelling), and believe you when you tell me you did your best. I ask for reassurance if I start to feel neglected or avoided or whatever, and I trust that when I do, you will tell me truthfully if you don't want to do the thing with me or if you didn't have the energy to do it. I will warn you if I need to keep to a particular schedule and if so, I will just continue without you, with no resentment. If I need someone to be there no matter what, I will tell you ahead of time and check in the day before to get a more accurate prediction of whether or not you will be up for it. If you are not up for it, I will find someone else to go with me or I'll postpone. I look at it like I would weather. It's just not something you can control and predicting it is notoriously unreliable. And I do this for nondisabled people as well because you can't have true consent if saying no at any point would result in punishment (pouting/passive-aggression is certainly punishment, btw).
For me, I forget things and run out of time despite trying my absolute hardest, and I need people to be understanding of that. My memory is so awful now that I often can't tie a person to a memory. So I will remember that someone I love deeply is allergic to that flower that starts with an H and is red, or that someone I love adores a particular band, but I often can't remember who. This is another thing that is often conflated with love, and I DEFINITELY used to do it. I used to express love by carefully memorizing things and mentioning them later when they were relevant. Now I worry people won't feel loved because I won't be able to remember the right things. I still try just as hard and care just as much, it just doesn't work. (I started keeping a list on my phone of things people especially love. Hopefully that will be helpful to my memory, since seeing things in print often helps me remember better than hearing them.) Unless it's in print or photo, I have ZERO control over what falls out of my sieve of a memory, and some of my most treasured experiences are gone. I may forget the best thing we ever did together if neither of us takes photos or writes it down (even then I'll forget until I read it or see the photos). That is unbearably tragic to me and I try not to reflect on it. Please, never assume that I love you less because I forgot something. It could literally be the best thing to ever happen in my life and I might still forget it. There are countless meaningful comments, emails, and messages that I have forgotten even though I appreciated them immensely. So many things I planned to do but forgot. And I put so many reminders on my calendar already, it's just not possible to do it for everything. And then, sometimes I fucking forget what I was doing when I pick up my phone and my intended reminder never gets made!!!
When I say run out of time, I mean that I planned enough time and then some, but then my brain wasn't up to the task, and it took an extra 10-30 minutes because I kept forgetting things and going back upstairs or back in the house, or I drove right past the exit, or I forgot that I was almost out of gas, or I got hyperfocused on something and lost the time (rare because I usually refuse to get deeply involved in anything before a plan, for this reason) or I forgot to eat and was feeling shaky and dizzy and unsafe to drive and had to sit down and eat a few bites to be able to go, or I forgot why I set my alarm for that time and snoozed it too much until I realized in a panic why it was going off! I have planned for an hour extra time and still been late (because I ended up hitting traffic or something). It is not lack of care or effort. If I say I care, I'm not fucking lying. And if I make a plan with you, it's because I love you enough to deal with the stress of trying to corral my brain and enough to accept the drain of energy it takes to go out (for so many reasons, not the least of which is my needs-repair car and the expense of gas) and/or give you my full focus. I am really fucking careful with how I plan my time.
*I mean, I'm sure there are some uncaring disabled people who like inconveniencing others and just don't value the time of others, but I've never met any. I haven't met many non-disabled people like that either. I think my pile of oddities scares off most of the people who are uncaring.