People calling a big bet instead of a small bet?

[PokerEveryDay]

Since I think too much I need some help. Sometimes when people make a big bet (NLHE) they are either bluffing or have the nuts. On the other hand that same person might bet small (not a post oak bluff though) and that looks like he is strong but maybe not. Do people (human instinct) like calling the big bets more than small ones because of the thrill of it? I'm also talking online play vs. live.

Thanks