I must be doing something wrong

Arduino: 1.8.5 (Windows 10), Board: "Arduino/Genuino Uno"

Sketch uses 928 bytes (2%) of program storage space. Maximum is 32256 bytes.
Global variables use 9 bytes (0%) of dynamic memory, leaving 2039 bytes for local variables. Maximum is 2048 bytes.
avrdude: verification error, first mismatch at byte 0x0000
         0x00 != 0x0c
avrdude: verification error; content mismatch
avrdude: verification error; content mismatch

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.