Be staring somebody in the face
Definition 1 of 2
Pro Tip 1/3Missed Obviousness
Sometimes people miss something right under their nose; this phrase highlights that oversight. 
The keys were staring her in the face, yet she searched the whole house.
Pro Tip 2/3Sudden Realization
Use this when someone finally notices something that should have been obvious all along. 
After hours of work, the solution was staring him in the face.
Pro Tip 3/3Metaphorical Use
The phrase isn't about actual staring, but about realizing something is very clear. 
With all clues laid out, the truth was staring them in the face.