〜だけに
all the more because; as you'd expect from
Plain form + だけに (な-adj + な · Noun + な / である)
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だけに says a result is stronger because of the circumstances: 期待していただけに、がっかりした, "precisely because I'd been looking forward to it, I was all the more disappointed".
The first half is a situation that intensifies the second. It works for disappointment, shock or joy: 高かっただけに、壊れたときはショックだった.
It also means "as you'd expect, given that": 十年日本に住んでいただけに、日本の事情に詳しい, "having lived in Japan for ten years, he knows it well, as you'd expect". In this use it overlaps with だけあって, which is only ever positive.
Compare ばかりに, which blames one thing for a bad result, and だけで, "just by".
Examples
期待していただけに、がっかりした。
Precisely because I'd been looking forward to it, I was all the more disappointed.
彼は十年日本に住んでいただけに、日本の事情に詳しい。
Having lived in Japan for ten years, he knows how things work there, as you'd expect.
高かっただけに、壊れたときはショックだった。
It was expensive, so it was all the more of a shock when it broke.
若いだけに、覚えるのが早い。
Being young, they pick things up quickly, as you'd expect.
一生懸命準備しただけに、合格したときは本当にうれしかった。
I'd prepared so hard that passing made me all the happier.