I like Littlewood's three principles of real analysis
Every measurable set is nearly a finite sum of intervals
Every L_p function is nearly continuous
Every convergent sequence of functions is nearly uniformly convergent,
of which 2 and 3 are in fact Lusin's and Egorov's Theorems.
http://en.wikipedia.org/wiki/Littlewood%27s_three_principles_of_real_analysis
