similarities

I would like to understand what makes people think that things are similar. I list here some websites dealing about examples.
1
http://collective-thoughts.com/2007/12/04/social-media-marketing-is-similar-to-a-fishing-tournament/
2
http://www.school-for-champions.com/chemistry/baking.htm
3
http://bioenergy.checkbiotech.org/news/production_costs_advanced_biofuels_similar_grain_ethanol
4
http://www.helium.com/knowledge/81356-how-writing-a-novel-is-similar-to-writing-music
5
http://wiep.net/talk/link-building/why-buying-links-is-similar-to-covert-advertising/
6
http://www.moolelo.com/australia-similar.html
7
http://www.grandin.com/inc/animals.in.translation.ch7.html

ok, I'll be back soon!
(work in progress)