Doing what you said you would do when you said you would do it is one of the best virtues to cultivate. However big or small the deed, it subtly restores faith in humanity and engenders good will.
Conversely, its disheartening when someone tells you they are going to do something and then they never do it. I’ve been on both ends of this, and it feels equally bad.
When someone fails to do what they say, we tend to lose respect for them, and their credibility is diminished. When we fail to do what we say we will do, do they lose faith in us, we feel bad about ourselves and it bothers us, often endlessly.
The best thing to do is quickly assist when you offer to help someone. If you say you are going to send some information, do it that day. If you say you are going to make a helpful business introduction, do it within the week. You get the idea. The longer you wait the less likely you will do it. The sooner you do it the better you will feel. If this has reminded you of something you need to do, go do it now.