Many managers think that it's their responsibility to set objectives for their people.1 That's what happens in the overwhelming majority of cases. But if you allocate them, they are your objectives, not theirs. If your people fail to reach them for whatever reason, some might be tempted to say, “I always thought that was impossible”, and their commitment to them may be weak. But, if you agree to their suggestions, even if they are not perfect, their ownership of them will be much stronger and they are much more likely to achieve them.
Open an early discussion with each of your people with this phrase: