David Gilbertson made a lighting fast site and wrote a fantastic article about it.

Writing a fast website is like raising a puppy, it requires constancy and consistency (both over time and from everyone involved). You can do a great job keeping everything lean and mean, but if you get sloppy and use an 11 KB library to format a date and let the puppy shit in the bed just one time, you’ve undone a lot of hard work and have some cleaning up to do.

https://hackernoon.com/10-things-i-learned-making-the-fastest-site-in-the-world-18a0e1cdf4a7