Most of the answers to the questions that existed previously are changing today at a more rapid rate than ever before.
The answers in your field are changing day after day as you sit there. What was true a year ago may not be exactly so today, just as the value of what you possess today may not be same in couple of months or years to come.
Come to think of it, some years ago, the surest way to get a good job was to graduate from school with good grades. But I bet you, that is no more the order of the day Because there are dozens of brilliant graduates that are still struggling with their certificates
The only way that you can be assured of staying on top of your field is by continually taking new ideas and knowledge to compare it to what you know today.