Final answer:
AdWords clicks can differ from Analytics sessions due to various reasons, including visitors disabling JavaScript and blocking cookies, as well as the differences between clicks and sessions as metrics.
Step-by-step explanation:
The reason why AdWords clicks can sometimes differ from Analytics sessions in your reports is because of all of the above: some visitors may have JavaScript disabled, some visitors may be blocking cookies, and clicks and sessions are different metrics.
When a visitor has JavaScript disabled, it prevents certain tracking codes from executing, which can result in a click not being recorded as a session in Analytics.
Similarly, if a visitor is blocking cookies, it prevents the tracking of their session in Analytics, even if they clicked on an AdWords ad.
Lastly, clicks and sessions are different metrics because a click refers to the action of a user clicking on an AdWords ad, while a session refers to a visit to a website. It is possible for a click to be recorded without a corresponding session being tracked in Analytics.