"Falling behind" means not keeping up with something or not progressing as fast as expected. It's like when you're running a race and others are moving ahead while you're slowing down. This can happen in school if you don't understand a lesson and can't keep up with the rest of the class. Or at work if you're not completing tasks as quickly as your coworkers. Falling behind can make you feel stressed or overwhelmed because you're not meeting expectations. So, "falling behind" means not staying at the same level as others or not keeping up with a certain pace .