One question I've always had is why we say Modim Derabanan while the chazan is saying modim.We don't really do this for any other section in shmone Esrei so what is is so special about Modim. The answer is beautiful I'd like to first brings mashal to illustrate the point. If ones family takes them out to dinner, as soon as one sibling says thank it triggers all the others to say thank you as well. So too by Modim when we hear the chazan thanking Hashem we cannot just sit back and be quiet we have to exppress our thanks to hashem as well.We each have our own personal reasons to be thankful to Hashem so the chazan cannot possibly adress these reasons.I found this answer to be very inspiring and really makes me be appreciative.