In the post of @arcange, he shows that there are two rules to reputation:
// Rule #1: Must have non-negative reputation to affect another user's reputation
// Rule #2: If you are downvoting another user, you must have more reputation than them to impact their reputation
Rule #1 implies, that if you are upvoting a post of somebody with a higher reputation than you have, this has an effect as long as you have a positive reputation, with the impact depending on a) your reputation and b) your voting power. If this wasn't the case:
- How could anybody at the inception of Steemit get a reputation higher than 25 (as all start with this value)?
- How could someone with the highest reputation increase his reputation at all?