I thought so too until one day I suddenly found myself was able to access google.com etc. without any issue for days until I search some sensitive keywords when

I thought so too until one day I suddenly found myself was able to access google.com etc. without any issue for days until I search some sensitive keywords when I was in mainland China. So the blocking seems to be heuristic instead of a blacklist. And also it seems GFW is able to filter SSL contents as I have always been using HTTPS if I can.