What are the reasons for occasional erectile dysfunction, as in being a random event among many successful intercourse attempts?

Some times it works sometimes it does not. The control of erection is a very complicated system and can go wrong for many reasons. Your body is talking to you. Listen and take good notes. What were you eating/drinking/smoking before each problem for example. Share notes with your Drs or get back with us with your diary.

Being able to have erections and intercourse means the there the mechanism is intact. Intercourse also depends on other factors like, mood, fatigue, environment, partner etc. So relax. Pay attention to these factors- you should be fine.