Can you "accidentally" perform a mitzvah?

This question essentially boils down to: do motives matter in following Judaic law?

For example, suppose a Jew indented not to fast on Yom Kippur, but because of a busy day at work combined with forgetting to get groceries (idk, I’m making this up here lol), they never ate until technically it was permitted. Would this be considered performing the mitzvah? Is there weight given to someone who say, fasted for the purpose of observing Yom Kippur vs. someone who fell into a mitzvah?

I’m inclined to say they should be – it’s probably pretty easy to accidentally follow some mitzvot without even knowing you’re doing it – but I’m not sure what has actually been written on the subject.