Because you don't have a file called something.html in a folder called lessons in the same folder where you have index.html. Your code says that there is a folder called lessons in the same folder where you have index.html. Is that true? Please also note that Lessons is not the same as lessons. The capitalization matters. You can also try dropping the period before the /lessons if nothing else is working.
Because you don't have a file called something.html in a folder called lessons in the same folder where you have index.html. Your code says that there is a folder called lessons in the same folder where you have index.html. Is that true? Please also note that Lessons is not the same as lessons. The capitalization matters. You can also try dropping the period before the /lessons if nothing else is working.