It has to do with the stroke you make as you write. In all three ways that I know how to write by hand (full cursive, my actual current style, and print), crossing the ts and dotting the is is just the last stroke(s) of writing the word. The word is not complete until those are done, just like an A (if you write it as a ball with a tail) is not complete without its tail, and sword is not complete without a d at the end.

You keep track on your head the same way you keep track in your head that a word is not finished up until you have written all the letters in it. My first language uses accents, and it is the same process. And yes, you can forget, not just for longer words. Teachers would certainly mark it on homework and tests. I struggled with accents, in general, but just like learning how to spell a word, you just practice it when you get it wrong until you get it right and it becomes muscle memory for how you write that word.

My signature doesn’t, however, since I have not built enough muscle memory to reproduce it. Yes, it is technically cursive, so that part is easy to get right; but the flourishes that make it a signature instead of just me writing a word like every other kid who learned the same cursive style would aren’t muscle memory due to lack of practice.