For most cases that's true. Still, Wither explosions and the Ender Dragon can destroy obsidian. That's why most people kill the Wither using the Bedrock located

For most cases that's true. Still, Wither explosions and the Ender Dragon can destroy obsidian. That's why most people kill the Wither using the Bedrock located on the Nether roof. Still, no material is free from destruction using glitches and some technical users remove entire chunks of obsidian/bedrock to make their farms more efficient.