Though he’d made the point that the best time to rectify your character is when you’re young, R’ Salanter now goes on to show how we can still do it to one degree or another when we’re mature.
There are actually two ways to rectify your character: first by consciously and rationally deciding and resolving to only do good and beneficial things, which is fairly easy enough to accomplish (after all, many people resolve to do well professionally so as to excel, earn more, and advance their careers). Or you can also do it by elevating that resolve to a truly exalted and transcendent level through your emotions.
Being humble, for example, which is considered the greatest virtue (Avodah Zara 20b), is something that’s nearly superhuman and virtually unfathomable, given that reason would argue that it’s important to stress your status and capabilities in this world. Yet we can — and should — strive for humility even though it seems illogical.
But we’d need to do it another way. R’ Salanter offers that we can come to humility by calling upon our emotions rather than reason. For each one of us has his own emotional underpinnings.
Now, while there’s no denying the fact that emotional truths are often based on things that are actually untrue (like “unfounded” fears) there’s no denying the fact that those emotional truths are indeed valid for the person experiencing them. Though rational truths (like the effect of gravity) are objectively rather than just subjectively true, that doesn’t demean the validity of emotional truths.
The point he’ll make soon is that we can oftentimes call upon our emotions to affect our actions more successfully than logic and rational thought.