Zac Guildford's much-publicised battle with booze has put the spotlight back on young sports stars and the bottle. In the past five years, 25 professional rugby players have sought help for drinking or drugs problems.
Williams said professionalism and the length of the season meant drinking was no longer an option.
"You just can't do it any more - especially not at my age. Now it comes down to - do you want to be a social animal and have fun or do you want to be a professional rugby player?
"That is the cold hard truth and I just don't think you can do both. As a team, people don't apply peer pressure as much. It is your call to go down what avenue you want to go down."
Williams also revealed he did not drink after the 2007 Rugby World Cup defeat. "I knew I was so emotionally fragile that it could go pear-shaped. But put me after a championship win - I am everyone's mate.
"For me the biggest learning is, what is your emotional level going into a drink? If you are in an angry, frustrated, pissed-off mood when you drink, things can go wrong. But if you are relaxed, enjoying the buzz, it can be a lot different."
Clearly, not all players have the same experience or self-awareness of Williams when it comes to alcohol.
Many of his senior peers do: those older players whose careers began in less professional times have learned how to adapt and moderate their drinking. They haven't cut it out entirely, but they now have an instinctive sense of when they can have a few and when it might be appropriate to let the reins off.
Guildford is an extreme rather than an isolated case of a professional rugby player struggling with alcohol.
The last decade has seen the game's elite players come under the most intense scrutiny and higher professional standards adopted across the sport.
The New Zealand Rugby Union and the New Zealand Rugby Players' Association have worked tirelessly to fund and build education programmes that detail the dangers and effects of alcohol - both social and physical.
Expectations around behaviour have shifted: the old timers recall the "good old days" when they could hit the booze hard, trash a hotel room and not face any consequences.
It was, back then, just "letting off steam".
The technological and social media age has brought an end to all that and players, coaches and administrators are unanimous that professional rugby has sobered up.
The majority of players want to go down the avenue of responsible and moderate use of alcohol.
But significant numbers of players still battle with the bottle.
