I think Eliezer gave us some good advice for understanding some of his characters’ plots: “One way to fathom a strange plot is to look at what happened, assume it was the intended result, and ask who benefited.”
Quirrell knows how Dementors affect him, and he knows that Harry’s got a piece of Voldemort stuck inside him, so it was a reasonable guess that Harry might be similarly affected, and permanently, if he was exposed for long enough.
Quirrell certainly anticipated the possibility of failure — his experiment was orchestrated so that failure left him no further from his goal — and in fact, he almost did succeed; I think it is highly more likely that he was hoping for an easy route to victory that almost occurred, rather than that what happened was an unexpected side effect.
I think Eliezer gave us some good advice for understanding some of his characters’ plots: “One way to fathom a strange plot is to look at what happened, assume it was the intended result, and ask who benefited.”
Quirrell knows how Dementors affect him, and he knows that Harry’s got a piece of Voldemort stuck inside him, so it was a reasonable guess that Harry might be similarly affected, and permanently, if he was exposed for long enough.
Quirrell certainly anticipated the possibility of failure — his experiment was orchestrated so that failure left him no further from his goal — and in fact, he almost did succeed; I think it is highly more likely that he was hoping for an easy route to victory that almost occurred, rather than that what happened was an unexpected side effect.