I think how shallow you are depends on how hard you try not to be - does that make sense?
It's like being polite - nobody is naturally polite, they learned to be and then maintain it. I think that hypothesis covers those times when you know you're being shallow, but you don't have enough energy to want to be, er, deep. Sometimes you just wana go out and mindlessly window-shop, or something.
Of course, I am a great advocate of always trying *not* to be stuff like shallow or impatient or whatever, but sometimes, it's just going to happen. It also depends what you call shallow, as people's definitions tend to be wildly different, usually depending on what our particular definition will excuse in own own behaviour! ;-D