Very true.

But always trying to maintain a "pleasant manner" under all circumstances can be exhausting. There has to be sincerity involved else the other person can easily pickup on the fakery. On the other hand i have observed that even when it is obvious that the person is faking it (eg. social etiquette), people seem to be accepting of it in general.

Perhaps the quote, The secret to Success is Sincerity; Once you learn to fake that, You have got it made is true after all. Humans are complex social creatures.