The feeling of appreciating something is a wonderful one. Having experienced something and then noticing that you like it and appreciate it gives a lot of energy and joy to your life. Sharing this feeling with other people around you is a great to way to make the feeling even more strong. Especially if the thing you appreciate is a person. Showing and telling this appreciation to them will allows both of you to relish the feeling and create a connection between you.
However, if you are even a bit anti-social or introverted as I am, you might have sometime stumbled upon that showing that appreciation to someone might be difficult. Giving the appreciation is intimidating for me as I want to do it the best way I can. So I start to formulate and build an appreciation that will in the best way possible show the other person how much I appreciate them. This again hinders me from giving that apprecation as I might start to optimize it too much. Suddenly I find myself having an inner struggle of how to build that appreciation and then that appreciation feeling that I am having in that exact moment never leaves my head. The person that I appreciate will never get to be aware of how awesome they are, because I am struggling with my own things.
Instead of this happening, I have tried to give out appreciations immediately when they are happening as then they are the most authentic and also best way timed. Waiting to write that appreciation a little bit better or trying to formulate it in another way will take time, and during that time your appreciation will have changed and it wil be difficult to communicate the feeling that you had earlier.