Here, ul has 8 children(8-li) on total.
And, each li has 7 more siblings(i.e brothers/sisters). Now, suppose you want to identify the 4th li where only first li can be identified uniquely. To identify the the 4th li we can proceed as follows:
Identifying the 1st li element, via the xpath
//li[@class='classroomlink hidden-xs hide']
if we want the identify the 4th li then if we proceed by giving slash after it i.e
//li[@class='classroomlink hidden-xs hide']/
Then it will look for the elements inside the li. And so it is not possible to navigate to the 4rd li.
Here we can make use of the following-sibling to identify our element by
//li[@class='classroomlink hidden-xs hide']/following-sibling::li