For some reason, I found 腮 easy to learn. Saw it once, haven't gotten it wrong yet while SRS-ing. Even the pronunciation, which is a bit weird as the phonetic part, 思, is not that close to sāi.
And yet, there are other characters I can see 50 times and still not remember their meaning or pronunciation -- or both!
Just one of those things about learning Chinese I don't understand.