Q: I'm a senior manager within a branding agency and would like to know how to get successful, optimistic people to be realistic without damaging their motivation and confidence.
A: I assume that the problem that's prompted this question is an all-too-familiar one. Seen through the eyes of your designers, it's mould-breaking creativity being crushed by client conservatism. And seen through the eyes of the client (and through yours as well, by the sound of it), it's adolescent impracticality flying in the face of commercial realities.
So I'm intrigued by your use of the word 'realistic'. One person's realism is another person's cowardly compromise. As a senior manager, it's your job to decide whether your designers' recommendations are unrealistic because they are unworkable: greatly in excess of budget, say, or internationally unacceptable. Or whether they're unrealistic because, although on strategy, they ask just too much of your clients' imagination. (It's seldom quite as clear-cut as this, of course, which makes it even more difficult - but that tends to be the crux of it.)
If, in an otherwise admirable pursuit of originality, your creative people are ignoring basic and unarguable client practicalities, then it's pointless your demonstrating empty loyalty by championing their work. Your clients will have no choice but to reject it, their future willingness to consider unorthodox solutions will be blunted and their trust in your personal judgment will take a beating. Everybody loses - not least your creative people.
So be clear and firm when you point out the problems - but don't present them as the reason why your creative people need to start again but as a further challenge to their inventiveness. It makes an amazing difference. Invite them to think their way round these obstacles.
But do be sure in your own mind that you aren't using the word realistic to stand for that which you know the client is expecting and will readily accept. That's professional failure on your part. If anything's going to make your creative people lose their motivation and confidence, that certainly will.