People forget things. If someone agrees to do something but they don’t immediately reach for a pen to write it down*, you should work on the basis that they will either misremember what you wanted or forget about it altogether.
The worst place for this is in project meetings, where some poor soul usually ends up with the bulk of the new tasks. By the time they get given the fourth task they will have forgotten the first one, and they haven’t even left the room yet.
Don’t be that person. Turn up to every meeting with the means to record tasks, even if this is just a biro and the back of your hand. When you agree to do something, write it down immediately, even if you have to make people wait while you do so. Don’t leave the room until you have a clear list of what you are expected to deliver.
* or start typing on their phone/laptop – hopefully they are adding your task to a list, but they might just be bored and emailing someone, probably to apologise for another task that they forgot to start.