IMHO failed prophecies are the easiest to see. Millions now living will never die, 1975, the meaning of the word "generation", and now the way they are going to handle who the anointed are (I beleive they will need to revise this somewhat). They explain that things get clearer as time goes on, but that is just a pat explanation coming from a group who claims to be God's spirit directed organization. God's spirit directed them to tell me college education was dead works when I was a teenager, but now evidently God's spirit has decided that is not the case anymore.
The hard fact is, these things were "hard facts" at one time, believed in by the people as much as they believed in God or Jesus. These beliefs were found to be false, and explained away as "changed".
As long as the WTS asks its followers to believe everything written in their Watchtower magazine as the absolute truth you cannot question, then I cannot go along with whatever it is they are teaching because they can, did and will eventually change it.