What actual insight stems from meditation?

I woke up this morning with a lot of anger. There was no reason for it, I didn't even have particularly bad dreams, it's just one of those days.

I'm sure there is a secular, physical explanation. Hormones, the male period, whatever.

It makes me wonder.

2500 years of buddhist meditation alone, which supposedly not only calms people down, but gives them insight into "how things truly are", and what really goes on inside. Direct insight into the mechanics of the mind. Direct observation of emotions and thoughts.

Assuming that, in all that time, not everyone was a phony posturing jerk such as myself; assuming that a few of those people were close to "enlightenment" (whatever that is), there should be some useful advice gained from all that meditation, right?

Advice which does not boil down to the boring repetition of a religious doctrine. Advice for people who would never ever meditate, who wouldn't assume a lotus position if their life depended on it. Advice that actually helps.

I have a hard time finding that advice.