The Oracle of Omaha drops what may be the best career advice you'll get today.

Billionaire Warren Buffett, chairman and CEO of Berkshire Hathaway, learned a long time ago that the greatest commodity of all is time. That's why he is religiously protective of his own time by setting strict boundaries for himself.

This leads to a "Buffett-ism" that has garnered a lot of debate over the years since he said it. It's a quote about the difference between successful people and really successful people.

The mega-mogul said:

The difference between successful people and really successful people is that really successful people say no to almost everything.

No to almost everything?

That's a tall order. Most ambitious people are driven for results and doing more, not less. If you're an entrepreneur like me, you are relentless in your pursuit of capitalizing on every opportunity presented to you if it means growing your business and income. It could mean, in your own mind, having to meet as many people as you can to get there. That also means saying a lot more "yesses" than "no's." But is it sustainable?

Well, from a self-help standpoint, if people close to you think you're taking on too much and you've been labeled a "workaholic," Buffett's "no" advice should a bull's-eye to your conscience.

While it's true that many successful and high-profile entrepreneurs put in 60 to 80 hours per week, really successful people don't neglect their mental health and self-care or time with family, hobbies, or other interests. They recognize that if they can't take care of themselves, the business suffers.

That brings us back to Buffett's point. We have to know what to shoot for to simplify our lives. We have to know what to say no to in order to keep our sanity. This may mean saying no many times over to things that don't serve us and saying yes to the few things that truly matter to advance our cause and keep us balanced.

Steve Jobs once said, "I'm actually as proud of the things we haven't done as the things I have done. Innovation is saying no to 1,000 things."

As we near the end of the year, this is typically the time people start thinking about what goals to set for the new year. I have one suggestion to add to your list based on Buffett's advice:

Learn to manage yourself.

Notice I didn't say learn to "manage your time." No, because we can't manage time. There's no such thing. We all wake up in the morning with the same exact number of hours, minutes, and seconds in a day. We can't control time. As it ticks away, it's gone -- in the past, never to be reclaimed again.

Focus on what you can control

But here's what we can do, and is very much within our control: choose how to use that time by managing ourselves wisely.

A good example of this is how I manage my LinkedIn activity. I get about 50-75 requests weekly from people asking to join my network. Most are trying to sell me something and will attempt to invite me to meet with them to "network" and explore "mutual" opportunities.

In the old days, out of professional courtesy, I would reply to many messages in my inbox. I am now prepared to be assertive, set boundaries, and say "no" to people when I need to, so my time is protected.

Now, I'm not sure if this example qualifies as the "difference between successful people and really successful people," but here are the things I recommend you say 'no' to, based on my own observations of really successful people:

Say no to opportunities and things that don't speak to your values, or further your personal or organizational mission.

Say no to superficial networking. Really successful people don't network. They build relationships.

Say no to overworking by doing all the work yourself. Delegate instead and trust in others' abilities and skills to get the job done.

Say no to neglecting your deepest wishes and desires for what your want to accomplish in life. Stop accommodating and yielding to others' wishes and desires. It's your life, take control of it, and live your calling.

Inc