[Chekov doesn't want to discourage Kirk from throwing himself at a seemingly impossible problem, he's just very tired of getting nowhere with his own attempts.]
Most of my trying was in a different prison where failing had very few consequences. Here, I worry about the effect that disrupting the simulation may have on us; I think that experimentation is inadvisable.
[But he's a cautious person. Maybe what they need is someone who has a habit of throwing caution to the wind.]