Is this "should" presumption or an obligation? How can you tell the two in so many different context?
ex)People with insomnia often find that regular exercise helps them sleep better. But when you exercise may affect how well you sleep. This is because one of the causes of insomnia is an increased level of stress hormones...Try exercising right after you wake up, in the middle of the day and shortly before you go to bed. After a few weeks, you should be able to determine which time is best for you.