Ever try an all-in, and then think you can come back from it? There is no better way to frustration and the desire to BM your opponent than the thought that his build is unfair because your all-in failed and you couldn't come back from it.
This situation happened to me the other day when I did a Roach/Ling all-in against a Protoss FFE and then railed at the unfairness of a 2-Stargate FFE build. Now - if I had made Hydras, this would be much less of a problem. However, after spending that much gas on Roaches, and cutting economy to get enough Roach/Ling produced, there's no way to truly come back from mass Void Rays - Spore Crawlers get picked off gradually, as do Queens. The Void Rays deny anything else until you get swarmed by Gateway units (even just Zealots + Voids will kill you at this point).
What you have to remember when you choose that strategy is that if it fails, and you can't continue to push because he's hard-countered you (meaning his units will just crush yours no matter what you do), you might as well leave the game right then.