It maybe wiser to think about tomorrow and not just today. Sort of like when people walk they do not look straight down because they might bump into a wall or walk into a quicksand so they must keep looking forward to plan ahead and maybe that is what people should do about their days too.
Take joy in today, and relish all of the pleasures that it offers. But be prepared for what tomorrow brings. If you are prepared for the worst possible outcomes and braced for the toughest challenges, then you are ready to enjoy tomorrow as much as you have enjoyed today. Today is fleeting; like water through your hands, it is soon gone. There will be many tomorrows; are you ready for what they will bring?