Word for something obvious that you've never thought of?
Solution 1:
Not a single word, but a useful idiom.
Be (right) under your nose — Cambridge
to be in a place that you can clearly see
"I spent all morning looking for the book, and it was right under my nose the whole time."
"She shoved the letter under her boss's nose (= made certain he saw it)."
See more examples on TFD.