The difference between 'were' and 'was', when used in conjunction with 'if', is important. 'If...were', known as the hypothetical subjunctive, is used for purely hypothetical situations, i.e. those situations that are more or less impossible. Let's take a look:
1) If I was in charge of this department, I would recommend longer worker days.
2) If I (Chris@magoosh
) were President of the United States, I would cut income taxes.
The first instance requires a position that is attainable. That is we presume that the speaker could be head of the department. The second example, on the other hand, is a position the speaker would never hold. Of course, was the speaker Mitt Romney, one of the current candidates for President of the United States, to utter this sentence, then he would say, 'if I was President of the...' Meaning, that for him becoming President of the United States is not an impossible scenario.
Some other possible examples of the purely hypothetical:
1) If I were able to fly using nothing but my arms. I would soar over Yosemite Valley.
2) If we were able to end war, the world would be a better place.
As for your example: A recent and popular self-help book wryly notes that if adolescence was not so painful, it would have a droll comedic aspect, at least in retrospect.
Adolescence is a painful experience. Period. Therefore to imagine it as otherwise requires the use of the hypothetical, 'if adolescence were not so painful...'
Finally, do not rely on your ear. In most cases, doing so will only hurt you on the GMAT. What sounds good is often based on colloquial use of words. Were the GMAT a test of the colloquial (notice the hypothetical subjunctive), then using one's ear would be fine