No is a powerful word to be used in the enabling of people and organisations.
No, don't start that Project, concentrate on this one.
No don't pursue three vendors, work on the best two.
No we won't... Etc
It takes a strong leader to say no and focus your people's resources on a smaller number of projects or tasks. The easier, lower risk option is to take 'em all on, covering all the bases. That puts the pressure on them, increasing the chances of problems and mistakes.
Do you know enough, understand the risks to take the brave decision to say no and bear that risk to enable your people to be successful?