ISSUE: In a GUI project there is lots of calculation and works are needed to be done in background when necessary . So when a button pressed or a certain action initiate the GUI may stop responding for you.
SOLUTION: In default when a MFC project is created the GUI portion has thread. So make sure the other necessary works are done on another thread (eg: calculation, process, response , internet query ).
You can have a better and great idea about thread use in mfc from this simple post