III.D16: Thrilling Defined

Gaudium est lætitia concomitante idea rei præteritæ quæ præter spem evenit. 

Thrilling is joy accompanied by the idea of a past thing which occurred beyond hope. 

Spinoza is describing a pattern in which not only are expectations unmet, met or exceeded, but also hopes are similarly unmet, met or exceeded. Here is where hope is exceeded.