"If it rains hard then the grass will be wet".
Many an early riser has found the grass is very wet but knows absolutely that there has been no rain over night. Does that negate that statement? Absolutely not, there was just a very heavy dew that night. It simply means that there are other ways to wet the grass. It could have been a sprinkler system.
The only way that conditional can be false is for T to imply F. In all of the other three cases the implication is true.