It really depends. A lot of them are hurt in some way shape or form and in a desperate situation like qooqie mentions and get pushed back into a corner over and over until they violently lash out, and a lot of others have a genuine disdain for other people or a warped personality/prespective on something (like Elliot Rogers and his entitlement to a girlfriend/sex) and rather than try and quell it or get help, they let it fester until they eventuallty also lash out.
The end result is the same. Either they get inspired to do heinous actions because there’s no other option in their head to stop whatever they precieve as a problem, or they look at someone else that did them before and think “they had the right idea” and emulate them.
Eh, easy mode is for those who need or want to use it. Ditto for hard or impossible modes. Adult, teenager, troglodyte, don’t really matter what ya are