That's bad advice to always go to social events. I tried to follow it in order to expand my social circle, but I ended up staying in places that sucked, with people I didn't like. I try to dedicate some effort to tell whether I actually want to attend or not, and then follow through. I follow my gut, but never change my mind after making the decision.
Of course if the only offer you get is places who suck and people you don't like, it's a bummer. Although I don't think the OP meant that - going for going's sake. In a hypothetical situation when the place would be just okay and the people too, some people's brains (mine too) tend to say "meh don't bother, nothing stellar gonna happen anyway". That is the impulse we ought to fight: don't save yourself for exceptional events, but be surprised by the small pleasures in regular ones. And still avoid the bad ones, that goes without saying.
The reasons my brain comes up with for why I shouldn't go are just lies.
Just go. And take what you can get while the opportunities are still coming.