This is actually excellent advice, although may or may not be harshly presented depending on your perspective. Setting goals are probably the single best way to learn anything and get sharp in the process.

I am a CS grad and am 30 now and have tried to learn several things in the past that have interested me in a variety of areas. I remember a few examples where I would learn/pickup/read something fast and think that I understand it but I would truly understand it only when I took up an ambitious project that involved learning and applying something. And your mind is automatically focussed/sharp in picking up stuff when there is a goal in front. Otherwise, it may just feel like cramming. Getting sharp should be a by-product of doing something worthy and ambitious that is aligned with your interests.

Also, don't worry about mediocrity just as yet since you're just starting out. But I've seen a lot of guys getting cozy in a couple of years after they graduate and get a job. So, do keep lofty and aligned goals in mind all the time. You will surprised. And that will take you way above mediocrity while keeping you sharp and vibrant as a person.