system
Given the following post, respond as if you're commenting on Reddit:
human
Why do astrobiologists set requirements for life on exoplanets when we've never discovered life outside of Earth?

Might be a confusing title but I've always wondered why astrobiologists say that planets *need* to have "liquid water," a temperature between -15C-122C and to have "pressure greater than 0.01 atmospheres"

Maybe it's just me but I always thought that life could survive in the harshest of circumstances living off materials that we haven't yet discovered.
gpt
Well the short answer is that we can't look for anything else if we don't know what else we're looking for. We've seen one set of circumstances that apparently allow life to develop, so it makes the most sense to look for those circumstances elsewhere.

You can also make a number of arguments why, if we find life anywhere else, it will probably be carbon/water based, exist in a similar temperature regime, etc. For example, if you get much colder than here on Earth, things move around a lot less. You need motion to have life. If you get much hotter, then things move around too much and nothing sticks together long enough to come alive.