A clear sentence helps more than a louder version of the confusing one.

Volume does not add information. When someone does not follow you, the instinct is to repeat with more emphasis, as though the problem were attention rather than construction. But the words that failed the first time are the same words, now delivered with pressure attached, so the listener gets confusion plus the sense that they are being slow. Rebuilding the sentence is the only move that actually changes anything.

Next time you are not understood, stop and say it differently instead of again. Use shorter units, name the thing plainly, give an example. And when it is you who did not follow, say which part lost you.