Could you possibly be misremembering this rather famous quote from Gandalf about deciding what to do with the time that is given us?
“I wish it need not have happened in my time,” said Frodo.
“So do I,” said Gandalf, “and so do all who live to see such times. But that is not for them to decide. All we have to decide is what to do with the time that is given us.”
The Fellowship of the Ring, Book 1, Chapter II: The Shadow of the Past
While slightly different, it has Gandalf suggesting Frodo needs to be the hero even if he wishes not to be.
Another possible quote is the following by Gandalf to Elrond, discussing the inclusion of the Hobbits in the Fellowship over a great Elf-lord:
“It is true that if these Hobbits understood the danger, they would not dare to go. But they would still wish to go, or wish that they dared, and be shamed and unhappy. I think, Elrond, that in this matter it would be well to trust rather to their friendship than to great wisdom. Even if you chose for us an Elf-lord, such as Glorfindel, he could not storm the Dark Tower, nor open the road to the Fire by the power that is in him.”
The Fellowship of the Ring, Book 2, Chapter III: The Ring Goes South
Gandalf suggests if it isn't possible by the power of the mighty to succeed then Elrond should trust to the Hobbits and their close bind through friendship.
Otherwise the only quote that rings a bell (and is near the only instance of the word 'hero' in The Fellowship of the Ring) is the following from Elrond:
‘I think that this task is appointed for you, Frodo; and that if you do not find a way, no one will. This is the hour of the Shire-folk, when they arise from their quiet fields to shake the towers and counsels of the Great. Who of all the Wise could have foreseen it? Or, if they are wise, why should they expect to know it, until the hour has struck?
‘But it is a heavy burden. So heavy that none could lay it on another. I do not lay it on you. But if you take it freely, I will say that your choice is right; and though all the mighty Elf-friends of old, Hador, and Húrin, and Túrin, and Beren himself were assembled together, your seat should be among them.’
The Fellowship of the Ring, Book 2, Chapter II: The Council of Elrond
I have emboldened any of the parts I think I might be relevant. If you can think of any other details should neither of these be correct I would be happy to search more deeply for you.