Examples:
A soft-spoken person can be a foil to an angry person.
A wise person can be the foil to a foolish person.
A logical person can be a foil to an illogical person.
A kind person can be a foil to a hateful person.
A generous person can be a foil to a selfish person.
An objective thinker can be a foil to a person who relies upon subjectivisms such as personal opinions.
An Ethical Journalism can be the foil to an Unethical Journalism.
A reasonable attitude can be the foil to a an outrageous attitude.
Pity can be the foil to cruelty.
Elaboration can be the foil to brevity.
Warmth can be the foil to a chill.