Are you speaking/writing from experience?
Kind of a mix of first, second and third hand.
Based on what I've observed as an adult (see para. 3) and felt myself as a parent (para 2) I strongly suspect my father walking out during my O levels was a sub conscious act of "taking a hammer and smashing it all up". In good part becuase he could no longer cope with the pressures that they as a couple had piled on themselves in the name of sacrifice for the sake of the children. Things just came to head at a time when there was no "graceful-ish exit from chosen pressures" option left. So ...the sledgehammer was the last remaining tool on the table. By the time that happened I am not entirely sure if the aspirations were really about us kids anymore. I have the sensation that they had been absorbed into their sense of identity and self worth. If I ever bump into either of them, I might ask. 
When it was my turn to make mistakes with my son's education it wasn't money related. But I concrete life jacketed us, and talked myself into an unsustainable corner with DS's educational options all the same. I was lucky. Pure and simple. Becuase my (rather sterotypically Italian when it suits him) husband is the World's Noisiest Secret Drownee. Despite my best efforts, I couldn't not hear the rampant spluttering. The arm waving was pretty dramatic too. Even from the depths of my tunnel vision of the time, I was kind of forced to pay attention before any thrown in towels made an entrance.
Where I live you get an awful lot of people on the cusp of being able to afford international school. And a great many of them talk themselves into something unsustainable becuase the alternative really, really doesn't suit them. There tends to be clusters of some quite spectacular towel throwing in and self sabotage (much to the horror and shock of the other spouse), just as the eldest gets near to end of KS3. I think that point may be connected to a length of time where people start to run out of steam, and/or see a small window of escape before they become trapped in a hamster wheel where they have to run flat out to stand still until the bitter end for the youngest.
Sacrifice on paper is very different to the reality. On paper we'd all walk on burning glass shards to get our children what we have talked ourselves into believing they need. Back in the real world, many of us are still the same fragile mortals with "long term martyrdom" aversion that we always were. And most of the time I reckon our kids do better if we suck up our limitations, lower our standards and be "good enough" for the long haul ........ rather than burning at the stake for them, and then falling to charred bits before the finish line is in sight. Leaving them high and dry when they least expected or needed us to reveal our feet of clay.
It's very complicated this being a parent thing. we can set the theoretical bar so damn high. And when we (predictably) knock it off proceed to beat ourselves over the head with it. All while the kid is standing there muttering ".when you've quite finished making this all about you, I could do with a hand here..."
Well I say "we". Might just be me.