English Translation
If you were more patient, you would understand better.
Why is this not tu?
It could definitely be tú, and be translated as “Si fueras más paciente, entenderías mejor”.
However, since English does not make this distinction (anymore) it could also be a polite you (like when talking to an older person, or a higher-up) in which case the sentence would be “Si (usted) fuera más paciente, entendería (usted) mejor”. And, since the pronoun is not really mandatory, when you remove it you have the sentence you encountered.
I observe many occurrences of redundant personal pronouns, especially él, and I believe this can often be explained by the psychology of translation, i.e., the wish to stay as close as possible to the original sentence (in English). That said, I see surprisingly few uses of explicit usted and ustedes. It would certainly help if these two were used more frequently.