Your logic is flawed. You can no more try to get praxis tha you can any other item because it is all random. Setting a goal of specific loot is insane as you have no control of the outcome
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It's not insane, people make these kind of goals all the time, in this game and many others (aka. shiny hunting in Pokemon). You can't always control the outcome, but you can improve the chances in various ways, such as doing the nightfall each week or buying the chest engram from Xur when he brings it