This means that whatever you do now it will affect u either in a positive or in a negative way.. like depending on what you do like wether u study or don't study at all all ur destiny might be that u passa a text or u don't pass the test. many ways that u know what will happen is when u do something good or bad. knowing what ur gonna do always requires u knowing what will happen and if it will affect u in a certain way. many kids in high school or in middle school have to focu on the decisions there gunna make ans what will happen after if they do that . more importantly this quote is to warn u that if u choose the bad things the destiny will me back. also if u choose the right decision it will help u out a lot.
An example is actions have consequences.
