The main difficulty here is the possible confusion between ‘complimentary’ and ‘complementary’.
• Complementary comes from Latin completum meaning “complete”. When one thing complements another it completes it e.g. in Mathematics ‘complementary angles are two angles that add together to complete an angle of 90 degrees’. ‘Complement’ can describe a number completing a full group e.g. : ‘This ship has a complement of 35’. Complementary can also be used to describe a wine that ‘goes well with‘ or ‘completes’ a particular meal.
• Complimentary is derived from the French ‘complimenter’. It has two meanings: a remark of praise or admiration about someone, or a courtesy gift or token. It would be important not to confuse a complimentary bottle of wine (a free gift) with a complementary bottle of wine (one that goes well with the meal but has to be paid for). In this context the ‘comments that worked wonders for the team’s confidence’ would have been ‘complimentary’. A second difficulty here is the possibility of using the wrong ending ‘complimentery’ or ‘complimentary’. However, there are many irregularities with the suffix ‘–ery’ or ‘–ary’ and the spellings of these words are best learnt by heart.