Here's why:
* Noun: A noun names a person, place, thing, or idea (e.g., "The surprise was wonderful").
* Verb: A verb shows action or a state of being (e.g., "I was surprised by the gift").
* Past Participle: A past participle can act as an adjective (e.g., "a surprised look") or part of a verb phrase (e.g., "I have been surprised before").
If you want to use "surprised" as a noun, you could use the phrase "a surprise" or "the surprise".