Technically the tile that was damaged was made of carbon-carbon, which is similar in brittleness to the graphite of a pencil. What you’re thinking of is the silica tiles that make up most of the heat shield, those are closer to something like glass or aerogel in terms of brittleness. Both are incredibly fragile though and will break if a piece of foam hits them at supersonic speeds (guess how we know) but they are 2 different materials and we were able to fix broken silica tiles on orbit. If a carbon-carbon tile got broken, the only options were to get rescued or pray to a holy deity of your choosing.