Plutarch, The Life of Cato the Younger 20

Though many invited Cato to become a tribune of the people, he did not think it right to expend the force of a great and power­ful magistracy, any more than that of a strong medicine, on matters that did not require it. 

And at the same time, being at leisure from his public duties, he took books and philosophers with him and set out for Lucania, where he owned lands affording no mean sojourn. 

Then, meeting on the road many beasts of burden with baggage and attendants, and learning that Metellus Nepos was on his way back to Rome prepared to sue for the tribune­ship, he stopped without a word, and after waiting a little while ordered his company to turn back. 

His friends were amazed at this, whereupon he said: "Do you not know that even of himself Metellus is to be feared by reason of his infatuation? And now that he comes by the advice of Pompey he will fall upon the state like a thunderbolt and throw everything into confusion. It is no time, then, for a leisurely sojourn in the country, but we must overpower the man, or die honorably in a struggle for our liberties." 

Nevertheless, on the advice of his friends, he went first to his estates and tarried there a short time, and then returned to the city.​ It was evening when he arrived, and as soon as day dawned he went down into the forum to sue for a tribune­ship, that he might array himself against Metellus. 

For the strength of that office is negative rather than positive; and if all the tribunes save one should vote for a measure, the power lies with the one who will not give his consent or permission.