When you're up material? Assuming your opponent is in a tier to leave pieces hanging, we should be talking more than a pawn here, and following the first two rules should hold/build that advantage.

At least, as someone not even 900, closing an endgame when I'm already winning sounds like the easier part. But it's hard to believe that's all it takes to get to 1500, it is not my impression that 1300+ players are losing to big "whoops" moments.