Note that the die is thrown four times and the probability that is referred to is after 4 throws. It is likely that majority of the time the die does not land on 6. However, it is highly likely of getting a 6at least once in that 4 throws, as compared with not landing a 6 at all.
You can think of it in this way. Remember that the die must be a 6-sided fair die for the probabilities to be so.
The probability of getting 6 stays the same (hence 5/6 **4 --i.e. prob of not getting 6 stays at 5/6 for the 4 throws) but it is more likely theorectically speaking to get a 6. Like for example using some software or pseudo-random number generator.