The glass jar is cold. When hot water is poured into it, the inner wall will expand rapidly due to thermal expansion and cold contraction. But because glass is a bad conductor of heat, the temperature will not spread to the outer wall quickly, which will cause the inner wall to expand, while the outer wall will remain the same, which will lead to the glass breaking! You can put the boiling water aside for a while, and then pour a little into the glass pot. After preheating, the water will not break.