It can work without include_directories( ${OpenCV_INCLUDE_DIRS} )?

C++
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1

I comment include_directories and it also can work.
why?

https://docs.opencv.org/4.x/db/df5/tutorial_linux_gcc_cmake.html

cmake_minimum_required(VERSION 2.8)
project( DisplayImage )
find_package( OpenCV REQUIRED )
# include_directories( ${OpenCV_INCLUDE_DIRS} )
add_executable( DisplayImage DisplayImage.cpp )
target_link_libraries( DisplayImage ${OpenCV_LIBS} )