Here's why:
* Missing Subject: The sentence lacks a subject for the verb "seen". We need to know who or what is doing the seeing.
* Incorrect Tense: "Seen" is the past participle of "see" and should be used with a helping verb like "have" or "had" to form a past perfect tense.
Here are some ways to correct the sentence:
* "I thought of you when I saw it." (This uses the correct past tense verb "saw" and clarifies who is doing the seeing.)
* "I thought of you when it was seen." (This assumes someone or something else saw it and is more passive.)
It's important to be mindful of subject-verb agreement and proper tense usage for clear and grammatically correct sentences.