The Thais always look for a correct balance of these flavors in their food: sweet, sour, salty, spicy. This nam prik nam pla sauce, along with sugar, chilies, fish sauce, are typical table top condiments to season their food to their individual liking.
Nam = water/juice
Prik = chilies
Pla = fish
Nam prik = chili sauce
Nam pla = fish sauce
I personally (not being Thai) prefer to leave out the sugar from most savory food while Thais typically add sugar into most everything, even in their Chinese-influenced noodle soups!
Anyway, always good to see Asian food/tastes being appreciated in the west!
'Never eat more than you can lift.' - Miss Piggy