You shouldn't do things that may harm someone else's health.
Martin is looking after his little son at home while his wife is running some errands.
Martin wants to smoke the cigar one of his clients gave him as a gift.
Martin waits for his wife to return, then goes outside to smoke the cigar, because he doesn't want his son to inhale the smoke.
Martin smokes the cigar inside, disregarding the fact that his little son is in the room, which soon fills with thick smoke.
The health of Martin's little son is not endangered in any way.
Martin's little son inhales the smoke, which puts him in risk of numerous health problems and starts coughing.