Because the task ETA would be the same even if it is not on you at the moment.
I can see from your profile that you are a student. So, you will be mostly engaged with your studies and related assignments. Managing time comes when you are loaded with many tasks where you feel unfocused. and struggling to handle any of those tasks properly. Best way to tackle this situation is to prioritize your tasks based on the importance and time delivery committed. There are chances that few tasks depend on someone or something to act up on prior to you. And there are few which doesn't require any others' involvement. Latter one can be easily done now instead of postponing to a later date. But for the former one, you can still do something like, asking for updates from those persons where the task is pending or even trying to get help from someone if it is depending on something which you are not fully aware. Because the task ETA would be the same even if it is not on you at the moment.