This question can be answered in 2 very different ways;
physically, and
emotionally. One of the two is very simple, and the other is more complex and varied.
Physically I generally go, or more accurately, am in my bedroom , or in front of the tv computer (the thought process is usually "hey, I'm here, I can masturbate," as opposed to "hey, I wanna masturbate." Well, to be more accurate, the thought process is more akin to "Ug. Sparticus horny. Needs satisfaction." but that is besides the point.)
The much more important factor in this question is the mental one. What is the state of mind of this person. Why are they risking blindness for their own self satisfaction? The answer is most often dependant on who is doing the masturbating, and the situations surrounding it. For example, your average teen will often be doing it purely for the purpose of satisfaction of relieving the almost constant sexual frustration that is part of their average day. This will often be done with images of crushes swimming through their head. No, the other one.
Personally? I go into a vast wonderland of memories, and variations of memories, and wish for the happy times to come again.
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