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A person who is a fool would not be good at their job.
http://dictionary.reference.com/search?q=Fool
If he took risks where he or his workmates could get injured he would be a fool.
It may not be diplomatic to tell such a person in such a straight out manner.

fool
n.
1. One who is deficient in judgment, sense, or understanding.
2. One who acts unwisely on a given occasion: I was a fool to have quit my job.
3. One who has been tricked or made to appear ridiculous; a dupe: They made a fool of me by pretending I had won.
4. Informal. A person with a talent or enthusiasm for a certain activity: a dancing fool; a fool for skiing.
5. A member of a royal or noble household who provided entertainment, as with jokes or antics; a jester.
6. One who subverts convention or orthodoxy or varies from social conformity in order to reveal spiritual or moral truth: a holy fool.
7. A dessert made of stewed or puréed fruit mixed with cream or custard and served cold.
8. Archaic. A mentally deficient person; an idiot.