The worst thing you can do to someone who is striving to make positive change is to remind them of their past weaknesses or bad acts. For example if someone admits to their past errors, you don't say, "Yeah, it took you a long time to learn that lesson!" Instead, why not say, "How do you feel now? Let their progress be described by them, not you.
Sometimes the sensitivity due to weaknesses and error is so deep, that a wrong word or reaction can ricochet a person back to that problematic behavior rather than encourage their positive change and growth. Once, a long time ago, I was delighted with the progress I made with a personal goal. In an effort to continue that progress, I hired a personal coach. The coach's first response to me was that I was doing it all wrong--her negativity collapsed my progress and defeated me within minutes. I wasn't strong enough at the time to endure such negativity and lack of support. In many ways, the progress I had made was undone by that negative, insensitive response.
Similarly recently related to a tough challenge, a friend reminded me of how weak I was in that arena. Her comments were not helpful at all, but rather than moving backwards in this regard, I simply decided not to share this goal or progress with that friend, a friend who clearly didn't understand the sensitivity involved in the current arena. Similarly I realized I reacted all wrong to a friend whose on another goal journey--my friend's reaction demonstrated to me that I was insensitive and unknowing about her challenge, a challenge I've not experienced.
Facing challenging goals in life is tough and demands the best possible supports. Not everyone you love and know will be able to support you through these tough challenges because not everyone you love and know will understand your personal challenges and goals. Instead you have to seek out supports that understand, supports that will truly help you achieve that which you aim for.
As much as possible, seek to understand the goals and challenges your loved ones are facing. Ask them what you can do to help them and don't project your own experience on them. Similarly don't expect those you love to be able to support you as you strive to make positive changes and growth--seek out those who understand what you're facing and what you're aiming for.
Rather than "See, you were wrong," move towards "How can I help you achieve that which you hope to achieve." We can do this.