Winning is a fundamentally cruel business, and becoming a winner means shedding some of your best human qualities in pursuit of the prize. That’s the payoff, the price of first place. Nobody ever did it without some ruthlessness, or greed, or selfishness, or venality. Nobody ever came first at anything without cultivating a darker side. And ambition, as someone said, makes us look pretty ugly.
But it’s not an absolute price. Balance is everything. You can be a winner and still retain essentially decent core values, enough to outweigh whatever dark side of your personality you cultivated to get there in the first place. You can be enough of a nice guy for people to overlook your faults.
The reverse does not apply. The wholly nice will not succeed. The wholly nice exist mostly to be clambered over by the mostly nice, the fairly nice, the nice-ish, the not-so-nice, the plain horrid. Be nice: but perhaps not too nice.