Some people see it as though you never know what tomorrow holds. So if you have time to do what that you have to do tomorrow today, then you should go ahead and get it done. For instance, if you have some homework that you know you're going to have to do tomorrow and have time to do it today, you should go ahead and get it done. That way you have more time to do something for yourself tomorrow, which you wouldn't be able to if you hadn't done that homework today.
Other people look at it as though tomorrow may never come, therefore you should do as much as you possibly can today. No one likes to admit it, but you all know that death can happen at any time. You never know when you will take your last breath. You should always tell your family and friends that you love them today, for tomorrow you may not be here to tell them or it may be that they are not here for you to tell them how much you love and care for them.
No matter which way you look at it, you should try your hardest to get everything you can get done today. You never know what tomorrow may bring. That way you have time to do something for yourself tomorrow. Of all the things this statement could get across to you, just always remember to tell the people you care for just how much you care, for tomorrow you may not be able to tell them just that. Therefore, if you have to do something tomorrow, and have time to do it today, go ahead and get it done.