sudden
猝 centers on something happening abruptly and without warning: a sudden event or change.
猝 combines 犭 (dog/animal) with 卒, which likely contributes the sound ソツ and may carry a sense of abruptness or suddenness. The exact historical development is uncertain.
A wild animal (犭) suddenly (卒) leaps out: 猝 means sudden.
For ソツ, imagine a sudden event that makes you say "Sots!" (like a quick, surprised sound). The suddenness of 猝 is captured in that sharp, abrupt sound: Sots -> ソツ.