I have observed that the best employees, i.e. individual contributors, are those who always say "No.". By always negating everything, they put the onus on their managers to come up with irrefutable logic and nail down the specifications for tasks, so that they would not get no for an answer.
Unfortunately, such people are also not the best people to get along with.
However if you're looking to start a product company, hire only these naysayers as programmers. Optimisitc kids with stars in their eyes will overcommit themselves and be the bane of your scheduling endeavors.