Unfortunately you are looking at percentages as an absolute. In FFXIV there is RNG at play which means that there's only two true percentages - 0% & 100%, anything else is unreliable. For example, at 90% success rate you would expect to get 90 out of 100 successes, *however* it is subject to RNG so you could actually never succeed in 100 tries!

Every try is like rolling a pair of dice, if you get two 6s then you win, anything else is a fail. You could roll from now until Christmas & always roll double 6, or you could never get double 6. That's the Random Number Generator (RNG) in play.

TL;DR - Ignore the percentages unless they are zero or 100. It doesn't work how you were taught at school in this game!