"As a platform for learning, this is the single greatest job in the world."
He was referring to venture capital. In order to do his job - picking startups that will multiply the investments - Brad needs to constantly study new trends in technology.
You don't need to become an investor to apply a similar way of thinking. Your career itself can serve as a platform for learning.
Personal and professional growth should be a key factor in your decision-making. It should be considered along with the usual metrics (i.ex. mission, income, track record). The benefits are endless: Your thinking, your skills and your network will improve over time.
I'm not saying everyone should switch jobs constantly. Quite the opposite in fact. The learning curve will become steeper after you have 'paid your dues' in a company, meaning after you've proven your commitment and curiosity. If you are bored and feel like you are not growing, address the problem and do what you can to change the situation. If that doesn't work, quit.
You need to be surrounded by people that inspire you so that you will slowly pick up their habits. Learning isn't supposed to be about remembering. It's about action - how you apply your knowledge and turn it into skills.
I've been following this approach throughout my career. Some of the biggest and hardest decisions have been based on whether I still felt like I kept learning during a project. I'm in the middle of evaluating my current situation again and some changes will likely result from that.
Note: As a founder of a startup, you are naturally learning constantly. The only difference is: You have to do it at a rapid speed in order to survive.